You could try Iconians or Yor, they are as far as I can tell the weakest economy-wise. Together with tech trading off, that can be enough of a challenge.

I guess it depends where your own strong points are. Mine is economy, so I find those races a bit harder to play.

Custom race with no bonuses?

It must be the Altarians--they always get dummied, regardless of map size, in every game I play (with tech trading kept on, that is). Arceans never seem to do all that well either.

I would argue the Yor. Without tech trading, the Yor can't mass produce economic structures, a prerequisite for fully developing planets. You will not have the cash needed to maintain your planets without them let alone building up a military. The best you can do without tech trading is leaving some of your planets empty because otherwise the maintaince costs will probally kill you.

You also shouldn't bother researching factory techs because everything later than "collectives" is progressively worse in terms of maintaince. Basically, being competitive requires you to be good minimizing costs while zerg rushing your opponents before they can develop their worlds. If the Yor had more cash, I could see them being a good factory civ, but they can't do so while restricted to their current tech tree.

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P.S. The Iconians are a powerful civ, the AI doesn't play them well yet. Their "Organic Hull Plating" is both powerful and cheap (in terms of maintaince to hit point ratio). Their only flaw is they don't resize, but it beats all when used on huge hulls.

I think the Iconians have gone from weakest (in DA) to being one of the strongest races (in TA). I mean, organic hull plating is awesome, buildings that give +50% planetary economy? Awesome. Self-healing hulls? Absolutely, totally, unstoppably awesome. I had one loser game as the Iconians in which the Dread Lords, due to some passivity on my part, conquered all but two planets in a small galaxy. Those two planets belonged to me, and were defended by uber starships (like 200 beam defense and attack, 1000 hp each after they leveled about 20 times, and self-healing hulls). The Dread Lords sent wave upon wave upon wave of fighters with 100-300 beam attack, would do about 50-100 damage, then the hull would heal most of that before the next one attacked. I clicked Turn over and over for about 2 years, just to see if they would ever finish me off. They never could, and I couldn't take them out due to a totally hopeless economy (two planets to support two ships at 250 bc/week, read: -100000 bc and falling). I couldn't win an influence victory, because silly me, I turned it off. Military would require the Dread Lords to die. I suppose I might have won a Diplomatic victory eventually, if the Dread Lords decided to randomly make peace, as they occasionally do. None of the other races would have lasted ten turns in that situation. Plus, the Iconians start with a +20 morale bonus, and buildings that give +25% morale each, and farms. That allows them to have a great starting economy, then research their merchant complexes and your economy is amazing.

Anyway, that was a bit off-topic. I personally believe that the Krynn are the weakest when the AI plays (for some reason, it thinks that a huge ship with huge defense and only 1 beam attack constitutes a strong military). For me, the Torians are the weakest. I mean, +10 morale and population growth aren't exactly awesome race bonuses. Maybe it's just how I play, but I always get crushed whenever I use them.

The following assumes no tech trading, of course.

I agree that Iconians are very solid now, but not so much for the ship techs as the amazing precursor library/archives which are hands down the best research buildings in the game. As far as economy goes, I find the Iconians weak even with the Merchant Complexes because they are stuck with Imperial government (all due respect to Emperor Iso!)

The Krynn are incredibly powerful at econ because it is so easy for them to monopolize tourism. I agree the military AI could be better.

I think Torians have plenty of research capability. First, more +% research passives than any other race (45%). And their buildings are cheap to build and maintain, though less effective. The Torian AI does a good job of alternating between maximum and minimum research spending to get the techs it needs.

I think Arcea wins the weakest civ right now because of the -1 speed penalty. They just get outflanked on the colony rush. I think the Stellar forge should grant +1 movement to ships built on that world.

The Drengin/Yor/Korath are really weak now not because of their techs or inherent bonuses but rather because the AI is messed up and won't expand. I actually find the Yor to be strong economists in early game, what with their passives (45%!). Late game try to balance the budget on each world rather than pursuing a completely specialized world strat. The worst part of playing Yor is keeping those robots happy. After you build a Maintenance Grid, the only way to add to morale is to build a farm (stalk). Paradoxical to say the least. I always beeline for Harmony Crystals.