Commercial / seafaring. Why? Because commecial lets you keep a large army and expansion and no real money issues. Harbors are cheap! Commercial docks are cheap! Coastal towns are easily made into commercial powerhouses with this combo.
Seafaring is _by_far_ my favorite single trait. It lets you expand more early (your galleys are less likely to sink, as are caravels and even those teeny tiny boats (forget the name) ) All ships get an extra movement point. I'm not sure if ships are cheaper to build or not, but that extra movement point makes sub warfare possible. If you get Magellan's, look out! Destroyers have TEN, count them TEN movement points, standard crusiers 8, and carriers NINE! (With magellan's) All this equates to invasions happening faster..
With sub warfare, you can utilize economy of force. If you can sink all the transports / galleons before they reach shoreline, chances are the AI will send the escort home. Even if you lose the sub, sending back the escorts is a fair trade if you sink the transport.
Commercial means you can stay in republic a _lot_ longer. With this combo, I rarely switch to democracy, simply because with C3C, and the republic supporting units for free, I can advance just as fast as a democracy with less war weariness. Without commercial, I have to switch to democracy and risk rioting when my enemies decide its good to start a war (they always seem to do that _after_ i switch to democracy hmmmmm)
