Which one is better to use in ASP.NET MVC?
First of all, it could be useful to take in mind that ASP.NET MVC doesn't support, or better, doesn't has the postback concept..
It's still possible to use asp.net server controls in asp.net mvc, asp.net ajax it's one of them, but asp.net mvc it's made, it was thought, to separate concerns (views) and to be REST styled as close as possible, so taking this in mind the final thought would be:
Sorry for my english