Like i said he is probabbly the most versatile actor of the big four maybe just on par with Keaton. he (Kilmer) was awesome in Tombstone as Doc Holiday was great as Jim Morrison in that crazy film and was also great in Alexander as the crazy father. Kilmer can do comedy and light hearted roles too such as Magmardagan in the awesome classic Willow and that guest appearance in entourage as the zany drug dealer.
Keaton is another versatile actor:Beetlejuice,Mr mom,that small role in Much Ado About nothing,Multiplicity,One good cop,Desperate measures i could go on all day.
Geoge clooney is a good actor but one i think who relies on playing the same kind of character (the charming good looking guy) in different situations but it doesnt mean he wasnt great in films like Good night and good luck,Out of sight,Syriana,welcome to collinwood and Solaris. Clooney had the potential to be the best of all actors to play batman but i believe no one could have saved Batman And Robin and he was still slightly green as an actor when he got the role (remember that annoying head nodding that he used to do whenever he uttered a long sentance?) He could have owned Batman Begins if he was younger and at this stage of his acting performances IMO.
On the Basis of films done Bale is probably the weakest but he is relatively young compared to the others though he will probably never become as famous an actor (IMO). Great films from him include the machinist and American phycho he was also good in equillibrium.