Manchu is bit hard to start and will have large money issues if going colonization route. But it's quite manageable and fun.
May two favorite nations, however, are Morocco and Poland. First is well suited for trading, colonization and conquest, in no particular order, plus Iberians love you (and your lands). Second has very interesting position and can both become the Emperor or simply dismantle the HRE, conquer or convert/vassilize Russians, and colonize a bit into the horde lands. I love focusing on production as Poland and completely avoid colonization. Poland was fun in previous EU titles as well.