Should I play Dread Lords first, or the expansions

There are pros and cons of each method. I'd probably suggest you play Dread Lords first and then move on but it wouldn't be a big mistake just to jump in and start playing ToA.

The only thing I wouldn't recommend is to start with Dark Avatar first but that's just my opinion because the nerfage of ship speed in that version of the game just makes it kind of annoying to play. With that said the version of the game that I'm currently playing is in fact Dark Avatar, so go figure.

I have a follow-up question. I have been playing ToA, but began with the Dark Avatar campaign. I noticed that it is using the unique tech trees of ToA, and am curious to know if this will not skewer the experience as DA was not designed with them in mind. At first I paid no attention, but on hindsight, and just finished first two scenarios, I wonder as perhaps I am getting more than the expected loss of buildings (incompatible with my race and hence unusable) after conquering a planet than was planned for in the DA campaigns.

These aren't the kind of expansions that just adds a few things, each expansion is really the 'current' version of the game.  There is no reason to play anything other than Twilight of the Arnor, especially since that one improved the graphics quite a bit.

That's strange because each version of the game has it's own separate directories for custom race configs and other game files.

I actually have never played a campaign nor have I ever played ToA other than to test out that my installation of it works so I really can't answer your question but on the face of it I wouldn't think anything you've played in ToA should change how DA operates. Perhaps someone else maight know for sure.

I think I've read that comment before, that some of the older campaigns can not be played as intended if you play them in ToA.

That being said, why don't you play the Dark Avatar campaign under Dark Avatar, that way it definitely works as originally designed?

I was going to make my own thread, but maybe I'll just add on to this, hopefully this isn't too much of a hijack.

I recently purchased the ultimate edition and am primarily looking forward to the sandbox play while finding the hardest level of game play available (looking to play on "tough" difficulty).  I've been reading all over trying to figure out which game is the best from an AI perspective, but get mixed feedback.

Dark Avatar was still a bit loose on the trade AI.

TOA has problems with tech scaling that screws up the AI and seems to have some other tech tree related holes?

The original seems to not get many AI complaints, but lacks the updates that the expansions brought.

So from a challenge perspective, any thoughts on which version is best?

I'd still say ToA because some races can be quite tough to beat (depending on galaxy size, which other races are in the game, etc.) and as a player you're much more constrained by the economy than in DA or DL.