Seafaring is my favorite trait, so my favorite civ is naturally a seafaring one, and in fact I'm sure my personal top 10 list would be dominate by the Seafarers. Carthage and the Byzantines are constantly fighting for #1 with me; Carthage brings probably my second favorite trait (Industrious) to the table, along with what I think is an underheralded starting trait combo: Alphabet and Masonry. Do you realize you're only two researches away from Currency that way? Getting marketplaces that much earlier, AND a tech monopoly on such a valuable tech (and perhaps on math too!) makes it pretty easy to fill out the rest of the tree via trade. Downside to Carthage is that its UU is expensive, unavoidable, and thus will trigger an early, perhaps even Despotic, Golden Age (although at least it'll hold your ground; being the best defender of the Ancient Era).
The Byzantines counter with Scientific (probably my third favorite trait behind Seafaring and Industrious), which is powerful in many ways, and the Dromon, which is probably my favorite UU and could possibly be the best. Especially when you are a Seafaring Junkie who loves to play archipelago.
And while Militaristic is one of weaker traits in terms of game mechanics, its probably the best/funnest trait in terms of "getting into character". While I'm pretty militaristic in my strategic approach anyway, it's just plain more FUN, for some reason, to play a militaristic civ and take that approach. Throw in my good friend Seafaring, and another "perhaps the best" UU, and you've got the Vikings, another favorite civ of mine, (though I'm cooling off on them as I inch my way up the difficulty ladder).
The raw power of the Agricultural trait puts the Dutch up there too, along with another factor: The Agricultural and Seafaring trait combo is very good at AVOIDING triggering golden ages via wonders. So you can build them and not get that undesireable early GA. Unless somebody attacks you in the middle ages and runs aground on that 1/4/1 defender, but again, it comes in the middle ages and is contigent on a strategic resource, so you can avoid it until you're ready for the Golden Age too.