Ehh... I guess I'm a generalist when it comes to US Type coinage, although I really love certain denominations more than others and would probably be happy concentrating on those... but... there are SO many other cool US Type coins out there that I simply can't do that!
My faves for US coins are Mercury dimes, Bust halves, and most of the early 20th century gold types. I only own one gold piece, a $20 St. Gaudens from the mid-1920's which I got as a birthday gift from my wonderful significant other. I admire the $2.50 and $5.00 Indians designed by Bela Lyon Pratt and the $10 Indian gold piece designed by St. Gaudens. My favorite early 20th century commemorative halves are the Oregon Trail half and the 1935 Connecticut Tercentenary half (I love that Art Deco Charter Oak design, for some reason). Oh, and the Pan-Pac type set from 1915-- cripes, does coin design get any better than that??
When it comes to ancient coins, I started out as a generalist, but I'm quickly realizing that due to the plethora of varieties, minting facilities, denominations, metals and countries involved, it's making more sense for me to specialize. But because I'm inherently curious and really drawn to cool numismatic artistry, I can't really specialize too much.
So, my current focus for ancients is twofold: to collect at least one coin from each Imperial Roman emperor; in ancient Greek coinage, to collect as many beautiful pieces as I can afford, no matter what part of the Grecian Empire they're from.
I love the coins of Grecian Syracuse, Thrace, Corinth and Asia Minor. So far, the Corinthian staters are pretty much out of my price range, but the others are probably doable within my budgetary limits.