I'm liking Portugal myself.

Early position is good with Jinetes and Javilinmen as your main forces, an easily defensible border between you and the French who are usually more concerned with the English and Milan and/or the Germans. Plus, you can make the Pope easily happy because you're able to attack vile heathens instead of your Christian brothers... after you launch a surprise blitz against the Spanish of course. The African provinces make for some slow crossing but after that the treasures of Egypt, etc await. Plus it's easy to get your merchants to some very profitable areas.

In the late game you've got Aventuros, one of the best pike units there is; Portugese Arquebusiers, one of the best gunpowder units there is; Basiliks, one of the best artillery units there is; Conquistadors and Knights of Santiago, some of the best cavarly there is; and Grande Carracks, the best ships there are... not too shabby.