Need advice on air conditioners

I need advise on the following. I'm looking at either a 2.5/3 Ton split airconditioner and in this specification, choices are quite limited. I currently have a 2 Ton Samsung split unit which is just not serving the purpose, and hence getting rid of it. I have shortlisted Hitachi/O General/Blue Star/Voltas in this specification. I find blue star to be comparitively cheap to the others, however im a little apprehensive about the service and support post sales in chennai. I have heard only good thing about Hitachi/O General however not too sure about the others in reliability aspect. Can any of you experienced people advice me on my decision? Thank you in advance.