Well, with this game picking a handful of characters isn't so bad because they take less time to 'learn' than other games. Also, because of the way the game plays, tiers aren't as big a deal. You can pick mostly anyone and do just fine.
A good resource would be:
http://ls57tiger.freepgs.com/jojo/phpBB3/viewforum.php?f=41
That link has character specific threads. Here's really quick notes from me though (for what it's worth):
Pucci: Doing his 'words' command costs meter now. Holding it down and getting multiple words does not cost additional meter. As enticing as it is to try and get "Made in Heaven", it is almost always not worth it unless it's a display of pure dominance. It's super risky to get, (getting all the words means probably going to final round, you'll probably have to sit on meter a lot), and although you can combo forever now, the timer ticks down even faster which is the greatest threat. Lots of characters have tricks to stall you out so it's a real hail mary as a comeback mechanic. If you try for the words, it should be to take advantage of C-Moon.
Josuke 8: Look up his combo that involves his HHA. Hits like a train. Be careful when playing as him because a lot of his stuff seems really punishable. As an extra word of caution, his move where he covers himself with bubbles has a silly weakness: If you run into him while he's doing it, you'll take little damage but recover before he's done his animation. This leaves him wide open for a throw/combo.
DIO you'll have to look up, I know little about him. But I will say: His MUDA MUDA is more punishable than it looks. Also, his 'sexy walk' move is SUPER punishable. Whenever I see a player use it I just duck and it will whiff entirely. Be sure its going to work.
EDIT: The H version is a command throw. So ducking isn't a good option. You can move in the many other directions though, and it's tracking is bad.
Kakyoin: He's one of the few characters that might not be best for beginners. To do well with him you'll have to have good knowledge of all his stuff, plus good knowledge of the character you're fighting. You need to take advantage of his range and punish every single mistake your opponent makes. Also, his emerald splash isn't as amazing as it first seems. It comes out slower than a lot of other projectiles. Projectile wars aren't great for Kakyoin, so you should stay at mid range for most match-ups (though some will require to be far away, or even closer). His Soff 214A and Son 63214A are both throws, which follow the same rules except that they work on Iggy. The only way to knock Johnny/Gyro off their horses is with Stand ON. (2H, or 623A). His only good anti-airs are his HHA and especially his GHA. So that means you're going to have to get confident with rolling under or ducking jump-ins. This is probably his biggest weakness. Finally, Kakyoin builds meter really fast, so take advantage of 'safety cancels' , stand rush and quick stand on to keep his actions fluid and safe. The second post of this thread has a link to a Kakoin vs Jolyne set. It's from a previous version, but you should study it thoroughly for as many pointers as possible. Just a heads up, if lag is bad (it will be) Kakyoin is pretty much dead on arrival because he needs to be able to react to be in control.
Diavolo: His Bn'B: 5LMH > 236M > dash in while holding forward > cancel his RUN with 5LMH > 214M > walk forward a bit > 214H. A 300+ damage combo that costs no meter. This means you sit on your meter for whatever you need.
Gyro: have no idea, but there's a thread in the link I posted.
The characters I like to play: Diavolo, Kakyoin and Caesar. Recently picked up Esidesi, who is actually pretty cool.