I used
http://www.smrealms.de/ship_list.php for my run down on relevent Thevian ships.
Thevian Expiditer 180 holds, 9 tph. No forces or hard points. Can trade, stock planets. Cannot shoot enemy scouts or seed.
Ambassador has 30 fewer holds but comes with jump, hard points, forces.
Leviathen, more holds and 100 mines and 25 scouts.
WQ Resistance is a poor first trader but WQ has the Rogue and the Blockade runner.
Drudge is much slower but with 250 holds, 2 hard points and some forces. A little bit cheaper first trader.
Thevian Carapace 11 tph, 5 hard points, excellent hunter with 50 scouts and with 100 mines can mine very well. 30 holds so not a good stocker/trader. Second only to ITAC. Cara is the main upside to going Thevian.
TAC has speed but cannot seed.
Thevian Shield Disperser is trumped by the more powerful WQ Human weapon.
Thevian is not an all around race and they don't have the best of anything in any one catagorie. That is why I would like to see the ability of the Thevian ships expanded a little.
Some ideals:
Expiditer: Add a hard point and some scouts.
TAC: Add 5 drones.
Expiditer would be an excellent planet stocker/builder and the TAC could seed.
To me being able to stock/seed in a Expiditer and seed in a TAC would be better than removing the WQ weapon.