Because I'm bored, I'll give you my analysis
Buu: No, not tank like at all. Despite the fact that he has the most HP and can heal it, he also has the second highest speed (until super buu is coded in). The downside? Well. . . I haven't found it myself. Maybe the bad part is that his insane speed can be difficult to control at times (i.e while you're swooping you might have trouble aiming at the enemy.) Mouthblast is a very good attack. Somewhere between gallit gun and kamehameha, leaning towards kamehameha. THe candy attack is a good finishing move that leads to nice benefits (health or strength.) Problematically he transforms kind of late unless you're able to own+ candy 15 people into donuts.
Goku: He's fast, not the fastest, but still quite fast. Spirit bomb isn't really an advantage. You're more likely to get vaporized. But kamehameha is a great attack. He transforms at a mid-level PL, and when he does, he can teleport and kamehameha at the same time in addition to moving while it's charging, which is very nice sometimes. Solar flare can be a rare gift at times.
Vegeta: Just as powered as goku in terms of stats. He transforms a little later. The key to him is the fact that big bang and final flash NUKE. So you can take out pockets of enemies in no time, provided they're busy. The downside is you could never both using his wonderous big blast attacks against a human who is focused on you.
Gohan: Starts out at average speed, but when he transforms he's just as fast as Goku or Vegeta. He transforms VERY early. Masenko, at the moment, is a useless attack. Shield can be useful in a tight spot. Kamehameha once again, is a godly attack since you can run, fly, and jump with it. But his HP sucks.
Krillin: Crappy HP and average speed at the start, but after he transforms, he's the MAN. He gets good HP after his transformation as well as the hgihest speed in the game. Scatterbeam is a useful weapon sometimes. Kamehameha once again is a great move. Insta kill destructo disc is also nice. Downside? Well, good look getting enough PL to transform. It's a long, long journey, and untransformed ur weak as heck.
Freeza: Good HP, good speed. Mid-level transformation requirements. The laser and the disc is very useful, emphasis on the laser. The death ball can make a huge boom as well. Sadly he has no beam attacks and in my opinion can be awkward to control.
Trunks: Average speed, SLIGHTLY above average HP. He transforms very quickly. Burning attack can be a very useful move (blinds the opponent.) Finishing buster is OK. He lacks a good beam attack. He is tied with piccolo as slowest character in the game after transformation. He's not a very good character right now, which is why he'll get a sword in the next version.
Cell: Good speed, good HP, mid-level transformation. Wide variety of attacks. Overall nothing all that bad about him. Hard to define his strengths and weaknesses...
Piccolo: Wide variety of attacks as well (scattershot, special beam cannon, masenko, eye lasers.) Eye lasers VERY useful. Mid level transformation. Tied with trunks as the slowest. Has slightly above average HP.