Comparing top superstars is very difficult, when it is with multiple industries it is very very difficult. Malayalam and Kanada Industries stars are not in the top list as my ranking is all about the stardom, fame, earnings, and success (financial revenue). As these two industries are small by financial factors, even the top 5 actors will get difficult to find place in top 25 actors.Eg: Forbes listed top 100 Indian celebrities in which 45 cinema actors & actress are listed. Out of 45 only 10 are south actors, and first south actors able to get 17th rank among actors (overall ranking 28th). Nagarjuna & Genelia are among them but I excluded in this list because of age & gender respectively.Also some stars are well above in one language but not in the other, here we used combined success. Eg: Surya success is well below Ajith in Tamil and may not be in top 10 Telugu. Whereas combined value bring him next only to Vijay & Prince.
http://www.ranker.com/list/top-south-indian-actors-of-today-v1/bmaruff,
Ajith Kumar
Powerful, Stylish, and Talented hero with crazy fan following among mass as well as class.
Dhanush
National award winner, reached International stage through 'Why this Kolaveri'
Joseph Vijay
Arguably Mahesh Babu & Vijay should be equal, whereas Vijay's die hard fan followings in Kerala & Sri Lanka made him little above to Mahesh Babu. Also Forbe's List of Top 100 supported my list as well.
Mahesh Babu
His potential deserve the first place. Hope he will explore the Tamil market and reach the spot he deserves.
NTR Jr
NTR Jr. is so big among masses in AP. Still unknown to other Industries (Most of them confused with NTR Sr.)
Pawan Kalyan
Multi Talented man got no foot in other languages to reach the place he deserve.
Ravi Teja
Simple & talented hero. Gives great mass hits most of them were re-made in other language and shaped career of the actors.
Vikram
Power house of Talent. Vikram faces continuous flops otherwise he is nowhere comparable to this list of heroes.
Ram Charan Teja
Though he made himself familiar to Tamil audience through his superhit Magadeera ('Maaveeran' in Tamil), his fan following is not yet started in Tamil Industry.
Surya Sivakumar
Surya's rank in Tamil Nadu is No.3 next only to Vijay & Ajith. In Andhra his rank among other language heroes is No.1 (Rajini, Kamal are excluded)In Kerala among other language heroes he comes second next only to Vijay.And overseas reach of Kollywood films are higher than Tollywood mainly because of the Sri Lanka, Singapore, and Malaysian Population. Also the European & American reach also high due to the Sri Lankan Tamil immigration.