Versions of GalCiv2

Not really. ToA improvements make it difficult for me to play or even look at the original and first expansion pack,

I have to disagree. The original game and DA are simpler, features-wise, but simplicity is not a bad thing. In addition there are some irritating bugs with the TOA AI that are absent in the previous games. I personally still play all three, though Dread Lords much less then the other two.

What bugs are those (that are in TOA AI)?

The most serious ones:

• Some evil races do not colonize properly. In my games the Drengin are the only one severely affected, but others have reported the Korath and Yor behaving similiarly. I've had to switch the Drengin to a different AI personality in order to make them a competitor.

• Some races (Altarians, Korx, Drath, and sometimes Terrans) don't build a military until attacked - then surrender to the attacker. Not building a military is a valid strategy that many human players use, but surrendering like this is a bug or major weakness.  When the surrendering doesn't happen, they tend to build up very fast and become military leaders, so it is a working (and unique for the AI) strategy, but the surrenders are still a bug.

• The Torians and Iconians frequently leave many of their planets undeveloped, without any structures.

• The Torians and Thalans tend to expand like crazy and wind up with far more planets then anyone else. Usually, they don't become game-winners because of other factors like the Torian bug above, but it still tends to make them among the top players in a game. It can be annoying to always go up against the Torians and Thalans.

Other players have reported other AIs behaving in a bugged fashion, such as the Arceans failing to expand, but I've never encountered any problems with any AIs but the ones mentioned above.

The problem with the ai generally has to do with the new tech trees that were added particularly in terms of building stratagies.  

Some of the AI types seem to struggle depending on the setup i,e galaxy size, extreme planets or research rate, The drengin in particular seem to hate extreme planets.

 Also your play style tends to have an effect on how well other races do. i.e. generally if you trying to play good you defend/help like minded races early on particularly the torians and thalans as they have huge amounts of cash and late game they  can gain reasonable fleets which can help you out or be purchased/upgraded if you need them.

On topic i mostly just play TA although i have played DL game over last summer which reminded me how much stuff is in the expansions. also you know you can play the entire campaign in TA    

I agree. I JUST got ToA and I don't think I'll ever go back.. lol

I strongly recommend you do not play the Dread Lords campaign on either expansion unless you're prepared to edit several of the scenario files to avoid bugs. Playing the Dark Avatar campaign on TOA is probably fine although I haven't tried it, as most of the bugs in the DL campaign were related to changes in DA - for instance, going from 10 to 12 major races.