I tend to like smaller starts with lots of options on how to play them. My top three would be:
1 - The Netherlands: Pre-CS, I tended to start as Friesland, now it's Holland, but whichever of the minors you chose, they're in a great position to do...well, pretty much anything. There's just so many options. You're in a great place to go colonising and/or dominate trade. You've easy access to some of the richest lands in the world should you want to build a tall nation. You're part of the HRE and can play the Imperial game should you want. You can get an extremely powerful, unique government with interesting mechanics, but you aren't forced into it, and can instead be either a normal monarchy or republic. And, just to keep you on your toes, there's the ever looming threat of the BBB.
2 - Milan: Much the same really. Small but rich, with all sorts of paths available to them, especially now that you can bring New World trade into Genoa. I slightly prefer the starting position and options for government (stay monarchy or go Ambrosinian) over the other Italian states.
3 - Yeren: When AoW first added the Manchu tribes, Yeren seemed to get overlook by many players in favour of its southern neighbours, but I've seen more and more posts on these forums recommending them recently, and with good reason. The start can be rough, as at times all four of your neighbours can go hostile to you, but at least you can now get an ally sometimes (Oriat), and once you get past that, there's plenty of ways to go. Manchu -> Qing is the obvious one, but thanks to being Animist, Yeren gets a couple of tricks up its sleeves. Reforming through the generic decision gives you the Muslim tech group, while, if you can wait that long, you can adopt Christianity when westernising. Expansion wise, if you don't feel like going south into China, you could sweep through the horde lands, and/or colonise the Siberian wastes. California and Alaska are also within easy reach, and trade from them can be rerouted to your homeland.