I play, mostly, as Taki, Yoda, and Maxi.
With Taki, I can keep you flat on your back most of the match, and I get a shit-ton of her air combos off before you even hit the ground. Furthermore, her diving attack and her bomb attack will seriously screw anyone over. Best way to counter me is with someone who has long reach, although it only lasts a short while.
If I'm using Yoda, again, better have someone with long reach, because the instant I get in close, it's an acrobatic display, and I tend to keep jumping out of the way of counters using the Force. Furthermore, don't swing high. I've found out how to counter/parry while in mid-air and attacking simultaneously. It generally leads into me grabbing you because your character can't recover fast enough.
As for Maxi...just don't let me get close or I'll be juggling you the entire match and you won't even be able to get a hit in edge-wise.