Which weapon line is the best?

There are developer posts floating around here somewhere analyzing that question: the short version is, at each level of technological development, the advantage changes. The first-tier missiles might be better than first-tier mass drivers or first-tier lasers, but the second-tier lasers are clearly superior to their contemporaries. The point being that, regardless of which weapon tech you pick, you'll go through stages of advantage and disadvantage relative to your enemies.

Also, you are correct to note that missiles tend to be powerful and expensive, while lasers are (generally) weak but compact. As I recall, mass drivers are cheap but bulky. That's an additional consideration.

I've gotten good results, not from looking at my opponent's defenses, but their armament. Simply put, if you note that the Drengin and the Yor both are focusing on missiles, you can safely bet that everyone else will defend themselves with point defense. Indeed, to protect themselves from each other, the Drengin and the Yor will get point defense too. If you are the only civilization in the galaxy using lasers, that can be a tremendous advantage, particularly since your opponents will be reluctant to switch their defenses entirely to shields lest the Drengin take advantage of that.

It should also be noted that missiles scale with hull size the least, which is a good thing if you are going to use the larger hulls a lot. I personally don’t like the massdrivers, but I’m willing to reconsider if anyone could make a good argument for them.

I personally don’t like the massdrivers, but I’m willing to reconsider if anyone could make a good argument for them.

Nano-rippers?

Well, in my current game I'm trying the laser line, but it seems like the lasers have a lot more weapons with the same name. I think I even saw Phasors VII! This makes me wonder if they will be able to keep up with missles at the end of the tech line.

My usual research line is to research missiles to the third of the second type (arg, can't remember, what comes between stinger and harpoon?). This feels like the shortest path to a 4 attack on a small hull and still have some room left over.

After that, I'll research the defense to the most commonly used weapons, and upgrade my 4/0 ships to 4/2

After that, I'll research Harpoons, upgrading the 4 attack to a 6 attack, and then research/upgrade the defense to 4 or 6.

About this time, the AI starts to figure out that Point Defense is a good thing, so I research mass drivers just far enough to get Nano-rippers, and then do some designs with a truely nasty sting.

I never take the gun class of weapon past nano-rippers unless both Point Defense and Shields are well researched and deployed in the galaxy and Armor isn't, as the upper end gun class weapons aren't as effective as the upper beam or missile weapons.