Just compare Surya's performance in kaaka kaaka with Kamal's in vetteiyaadu vilaiyaadu. We will know what acting is. Like i said Surya can be dramatic in his emotions at times that the flow of the role is gone, but that is if you analyse too much.
1. General Audience - Surya is certainly the next big thing if you try not to analyse his acting skills too much. He does have a presence.
2. Critics - Good but not great. There are alot of artificial or maybe the best word, limitations in his acting skillset that when you want to compare with actors like kamal and rajini, he certainly is not there.
In reality he is already the next big thing, in fact he is one of the few heroes besides kamal and rajini who can pull in housefull shows in singapore. But since we are using our own perception of his talent than anything else, i can safely say he still has a long way to go. Basically he needs to get it right for the sequences that requires him to be more composed.
Madhavan really impresses me more cause he makes the scene look impressive without having to be dramatic. He really makes good use of his body language, expressions in such a way that the scene is quite memorable but we dunt really notice his acting. Most of us here would scratch our heads when we see some of his movies but if you were to carefully look back he is so subtle that the scene does not lose its flow. It does not look impressive on first hand but he just gets himself in the scene without having to enhance it something like how rajini used to do for alot of films.