Industrious for sure, as darius explains.
And Ag is excellent, since food is growth is power (and it makes desert worthwhile.)
But i'm addicted to Rel's cheap temples too, expanding borders and culture-flips - one of the joys of the game. And the thought of wasting 7 or more turns just to switch govs... that could be hundreds of years!
How can you not want Sci's tech benefits? And rushing Wonders is still intoxicating, whatever leader does it.
But Mil really suits my play style more than any other - MGLs make Armies!!! and FPs! and barracks are must-builds for me anyway...
Seafaring won one game for me; it's really fun to dominate the seas, bombard coasts, invade at will...
Expansionist was my first favorite trait. Goody huts are actually good, early tech lead, and free Settlers! But it's for short games...
So - I can't pick just two. Sorry.
And probably Commercial is better than i think; i love extra cash, and if corruption really is lower...