My own opinion, I guess it depends on war or peace with whom? If your talking about the natives, the answer is easy: the French are the best for peace, as they don't irritate the natives nearly as much as the other nations; on the other hand, the Spanish are the best for war, as they have a bonus when attacking native settlements.
For war with the colonial powers, I'm not sure anyone has a clear edge. The English produce more colonists, but in my own games, my strategy has always been to fill my army with capture colonists from those attacking me, so I don't know that this characteristic really gives the English an edge. The Dutch have a more stable economy, so presumably they can sell more silver for longer (before the price tanks) and thereby have more money to purchase more guns and horses, which may make for the most powerful attack force. The Spanish, with the native-attack bonus, might fund their own war by plundering native settlements.
For peace with the colonial powers, I think it is much more a matter of what Founding Fathers you choose. I.e., Ben Franklin can get you out of wars, etc.
I hope that helps. It's been over a year since I've played much Colonization. (It was my first Sid Meier game. When I discovered Civ II, I was at first disappointed that it wasn't more like Colonization, with specialized citizens, more random distribution of specials, etc., but then I got into the tech advances, wonders, and such, and I have seldom looked back.)