The difference is the level
.in is 2nd level where as .co.in is 3rd level.
People like .in instead of .co.in
But by Search Engine Optimization you can get more traffic.
the level of a domain is not responsible for high traffic change.
Because seo is the best way for website traffic.
it's best to start optimising your new site and promoting. you should then start to see an increase in traffic. any tld can do well, it's just down to the efforts of the webmaster
.in or .co.in have nothing to do with traffic, if your site has enough killing instinct then people will remember it automatically after first visit. But still I think by using .co.in you can approach to global visitors also, with .in you seems to impress the Indian visitors only.