What I take a drop year for IIT or just go to VIT ?

You should if you're fully convinced and motivated. I'm not one of those who consider dropping out as a bad option. It is bad for those who don't have enough motivation and desire. If you're ready to give up every peripheral distractions and ready to work your socks off, you should drop out. Going to VIT is not a bad option, but is definitely an expensive one which might not yield as much after four years. However, spending some amount of money for dropping a year in coaching expenses and books and the securing admission to an IIT or even a top NIT will be a much better long-term solution in comparison to going to VIT.