For me its Aamir.
Aamir has played different types of characters and acted in different types of movies and excelled in them.
ROMANTIC- QSQT DIL DHKMN RANGEELA RH ISHQ FANAH MANN
COMEDY- 3 IDIOTS ISHQ
ACTION- GHAZINI SARFAROSH GHULAM DHOOM 3
PERIOD/DRAMA/SERIOUS ROLES- LAGAAN, TAARE ZAMEEN PAR, DANGAL, RANG DE BASANTI, P.K., 3 IDIOTS
SPORTS FILM- JJWS, DANGAL
COOL URBAN FILM- DCH
(NOTE- Here i mentioned only successful movies)
Aamir played roles from a teacher to student(tzp, 3i) from a rich man to a tapori(rangeela, ghazini) from a lover to a killing machine(qsqt, ghazini), from a patriot to a terrorist (rdb, fanaah) from a police to a thief (sarfarosh, dhoom 3), from a common villager to a urban guy (lagaan, dch), from an young alien to an aged wrestler (p.k., dangal).
Tranformation from a lover boy to killing machine in ghazini and from a fun loving guy to a responsible citizen wanting to bring change in RDB was only possible for this method actor.