The big problem with civilian tech is crystal. Unless you're on a map where you can procure multiple ice planets early and plant refineries on them, you just can't get this to work because you need many techs all with very high crystal costs. Moreover, like any booming strategy, if an aggressive player bypasses your frontal defenses you can be crippled before this pays off. If you can't get loads of ice planets, you'll be spending so much money on the black market that your military will suffer dramatically and any opponent who isn't an AI will be able to overpower you with ease. I should know, I fell into this trap when I was first learning to play.
Your best bet is, of course, TEC because they get so many trading upgrades and because you can research a discount for the black market (something you won't be able to avoid using to some extent because of the resource imbalances civilian tech focus causes). Advent also works because of their fast teching speed. It'll be slower to get off the ground, but once you have it off the ground it's research times and not cash that become the bottom line.
