Kevin Pietersen - One of the most aggressive, and the one who's likely to be more succesful and average 50+
Matthew Hayden - Hayden is not like some of the others where he trys and hits miles out the park. He gets a ball that is ever so slightly wrong and smashes it - brilliant.
M.S Dhoni - A typical keeper batsman with a ultra aggressive batting style. Has been successul on the rather pointless asian pitches, it will remain to be seen if he can do it on a tougher stage.
Shahid Afridi - An out and out slogger with no temperament, can be good occasionaly, other times not. Can keep his spot in the ODI team with bowling anyway.
Sanath Jayasuriya - The master of pinch hitting, and carried on that trend throughout his career - class.
Andrew Symonds - A big hitter who proved his class at the 2003 world cup, and has carried that on at ODI level but hasn't proved himself at test level, althought that hundred would of helped.
Out of the lot in terms or aggression + success I say Hayden would win. If we had all these plays at the end of their careers I reckon Pietersen could top them all in boths forms of the game.