I picked Scientific, simply because, in all my Civ experience and in all my experience with every other empire building / world conquest type game (e.g. MOO2, SMAC, RFTS, etc), The civ/nation/race/faction with the Science edge almost always wins.
There's /no/ substitute for knowledge, and knowledge is power.
In CivIII, it can likely be traded for things you don't have, too!
Now, I do think that Scientific has been toned down - the bonus is to building things like Universities, so there's no across-the-board increase in your Research rate.
Combine Scientific with Industrious (odd that that's not an option, eh? Gamebalance, I assume) and you'd pump out those improvements too quickly.
Combine Scientific with Commercial, and you can boost your Research rate... Dangerous.
Combine Scientific wth Expansionistic, and (with some luck) you'll be into the next Age before your opponents are even halfway through!
Russians, baby, yeah!!
- Stravaig
PS (I think the French are pretty awesome, too. It's hard to argue with the intense flexibility of being both Industrious /and/ Commercial)
PPS (Anyone know if Philosophy is still going to grant a free Advance?)