If I'm equally advanced in the weapons techs (can only happen if I've captured a tech as I stick to researching on one branch usually) I use a mixture as it is harder to defend against. Otherwise it is just the biggest bang per buck. This is usually guns as the cost of weapons on that branch is lower than the others.

The formula for defence is based on the full value of the specific defence + Square root of the other two. (E.g. If you have 1 point in each then the defence is 3 against all types of attack. If you have 4 points in each then you have 8 points of defence against all types of attack.)

The wrong defense is still a bit effective against any of the weapon types. It is calculated on its square root value, so you might get as much as 3 defense if you have say, 9 shield defense against mass drivers.

Also, consider what some of the 'special' ships are outfitted with.
The Lucky Ranger, one tough ship to kill, has only mass drivers and armor. But it still stands up pretty well to beams and missles.

In one recent battle of mine, I had outfitted a ship with very heavy armor only. The only weapons used so far in the game had been mass drivers. I was surprised to find some Yor fleets outfitted with some heavy missles when I attacked them. But those armor only ships fared very well. I did not lose a single one, even though the odds were around 7-1 with a few of the fleets. And this was in v1.2 beta with the new combat system.

I think in my next game I will test it out a bit further and only use armor only like the Rangers.

One advantage, if they survive long enough to take some damage and effect repairs, is that the hit points can get insanely high. Once the hit points are high enough it is nearly impossible to do enough damage to destroy them. If the defenses are so good that they take zero damage the experience does not count for as much, and the hit points don't climb as fast.

"I maximize weapons on ships.... to use up all the space... I hate wasted space on ships.... "

But then you also waste a lot of ships.
I tend to build ships that use defensive tech against the weapons the other races built to a certain degree while putting weapons in em that the enemy has no or little defense against.
Even if my weapons are not as advanced the additional defense usually keeps em alive long enough to finish off the enemy ships.

"The Lucky Ranger, one tough ship to kill, has only mass drivers and armor. But it still stands up pretty well to beams and missles."

HUH?! In the few cases I ever met a Ranger it was a piss pot with next to no defe or offence at all...

I chose quality over quantity.
In the beginning I just build one tiny fighter with only weapons and no defense or engines for each planet to stay in orbit. That way it looks like I have some millitary power and the AI can't use only troop transports for an invasion. Then depending of what's happening around me one or two squads of fast small fighters to intercept hostile freighters, troop transprts and constructors. But most of the time I research/trade up to Medium Scale Building and build frigates with at least one engine of the most advanced type. I keep an eye on possible agressors and what weapons they are researching. Then I add a defence of 2-4 (against the opponents weapons choice) and I go for one specific weapon type (again based on what everbody else is doing and choosing something different, of course).
I always try to research to the last tech of one tier (weapons/defense/engines) and/or the first of the next. This gives the most flexibility regarding the us eof space on my ships.
Normally I am able to build those right about the time the AI declares war on me.
Then I build squads consisting of these frigates and most of the time I don't fill up "left over" logistic points. Only if there is a tiny or small fighter at hand. Then it's time of guarding planets is over and he has to fulfill his destiny to fight fleets of superior ships and die for the glory his nation.
At least in the new combat system he gets to fire a shot before going to valhalla...

Oh, and after that I chose "Quantitiy". I prefer using only "more" frigates compared to "lesser" battleships in a squad. I take some time to research Large Scale Building. I focus on logistics.

It's been shown repeatedly that defense isn't worth having. Go all offense all the time. HPs just don't scale up enough to make it worthwhile mid to late game, so why waste the research.

It's been shown repeatedly that defense isn't worth having.

Oh, "the-defenses-are-worthless" thread again. (See also: https://forums.galciv2.com/?ForumID=346&AID=117458)

I tend to use a lot of defenses (matching whatever my worst enemy has) as soon as I have medium hulls, but not before that. Putting defenses on a tiny or small ship means it will either be slow or a weak attacker.

I'm curious what ship mixtures you folks use.

So far, I've tended to use the following ship types:

a) Warship - ships with whatever size hull I can manage with the best mix of weapons and defenses I can afford (I do like to use defenses to a degree).
Sensor Ship - a tiny hull, built to match the speed and range of my warships but loaded with sensors and no weapons. Using this ship gives me a decent sensor range in a fleet without having to build sensors into my other designs (and it only costs my fleets two logistics points). So far, I've found this approach is worth it since seeing what's coming at you is half the battle (then it's often your choice whether to attack or to run).
c) Interceptor - a tiny hull loaded with as many engines as it will take and light weaponry. I use small groups of these ships for attacking freighters and unescorted transports during wartime (their good speed usually allows them to escape from better combat craft and generally stay out of trouble).
d) Sensor Interceptor - Sensor ship (see b above) for escorting interceptors.

Obviously there are transports and colony ships too, but the above are my primary ship types.

Yeah Tiger I love my Small hull based troop transport near the end of the game with three troop modules my fav troop transport.

It's probably because I go incredibly diplomatic and research races, but I never seem to be behind the curve or even attacked until I'm prepared with large hulled ships capable of defeating entire fleets of what the enemy has. I usually research the final defensive techs and have them implemented before I ever have war declared on me. And I also go for two weapon researches. The reason? Simple, I think beam weapons look best, so they're always researched, and Missiles look cool firing simultaneously to Phasers on capital class ships.
My tiny hulled ships always have lasers, they're the escorts of the fleet
The small hulled ships always have missiles. I just love having a 'bomber' class.
Medium focuses on lasers
Large and huge have a mix.

Partly I justify it by saying that they never have the appropriate defenses for both weapon types (and sometimes waste space on their ships putting in defenses for both types), but the real reason is I just think it looks awesome.

I usually stick no defense on the tiny hulls, 1 on small hulls, 2 on medium, 3 on large, and up to 4 or 5 on huge hulls. I find this keeps my tiny ships first in line to get attacked, and they're easy to replace in fleets. I'll defend large ships because I'd prefer not to replace them. also, since the most powerfull attacker in a fleet is first targeted, if a fight is going badly, the AI's most powerful attackers will be destroyed by the time anything is shooting at my larger ships, and they can mop up the AI fleet while most of the attacks on them do no damage or a few hitpoints at best since the AI's heavy hitter ship has already been destroyed.

"I maximize weapons on ships.... to use up all the space... I hate wasted space on ships.... " But then you also waste a lot of ships. I tend to build ships that use defensive tech against the weapons the other races built to a certain degree while putting weapons in em that the enemy has no or little defense against. Even if my weapons are not as advanced the additional defense usually keeps em alive long enough to finish off the enemy ships. "The Lucky Ranger, one tough ship to kill, has only mass drivers and armor. But it still stands up pretty well to beams and missles." HUH?! In the few cases I ever met a Ranger it was a piss pot with next to no defe or offence at all...

I have not seen one show up in a very long time. And the last few times were when the weapons research had far surpassed them so I gave them away to minor races. So I know what you mean. In 1.0 they showed up much earlier in the game and gave a huge advantage, especially if you scored 4-6 of them.

I also make ships with defenses to match the most likely I will go to war with, and weapons that they don't have any defenses for. They are getting better in 1.2 at building the next round with those defenses now. So it gets harder to catch them unawares after that first strike.

I'll usually have around a 2//3 to 1/3 ratio of defense and weapons. With the new combat model in 1.2 it is a lot harder to keep all the ships intact during that first and second round of the battle. I usually have much fewer ships in my fleets, but they are more powerful. So sometimes it is 13 against my 3. And the ships are so costly (both time and money get real short early in a war) that I can't afford to lose any of them if I can help it.