i have been selected in vit,srm and manipal but my aim is iit should i take drop or continue with any of that college
If you think that your preparation is well enough to get you into IIT next year then surely drop will be the better option. If you joined any coaching institute previously then you get a rough idea that whether you may have that tendancy to clear JEE Advanced or not. First observe that zone.
Otherwise all the above colleges which you listed here are considered as one among the best private college so it will also be a better option to do your undergraduate UG Degree with these colleges.