Japan is a my favorite non-ptw civ to play. Usually you know early whether it's going to be a winner or not; the problem with Japan is that it often starts out in jungle-heavy turf, so the early going can be difficult. But if you make it to Chivalry in decent shape, you can go on a real roll; Samurai are the best all-in-one unit in the game, I think. Attack, defense, pillaging; they can do it all and they're hard to kill off.
Spain is fun in ptw; those conquistadors are great sport. Incredibly annoying to be on the receiving end, because they tend to swoop in and remove all your resources and workers in the first round of a war, while their dogs laugh at you, which can really suck.