IIIT

All of the IIITs that you have mentioned don't have their own campuses, so their classes are going on in the NITs of their respective states. The better of these is not a straight answer since there are no placement statistics as their first batch passed out this month only. Maybe you can check the stats in a month or so if and when released. Also, if you do think of taking admission in one of these colleges, I can only tell you that there is no discrimination on the basis of IIIT or NIT. Since I study in IIIT Una, I can tell you that NIT-Hamirpur has got a really good campus but you'll get bored if you are from a metropolitan city, since there are no attractions nearby and you won't be able to find your favorite fast food chains here.

Counselling and admissions process in IITs and IITs is offered by JoSSA. JoSSA is a committee, provides a single platform for admission process in IITs, NITs, IIITs and many other colleges based upon the rank in JEE Advanced and JEE Main exams. In NITs, IIITs, GFTIs and many other private college counselling will be based upon JEE Mains rank while in the case of IITs, it will be JEE Advanced rank. *Eligibility criteria to participate in JoSSA counselling process:
The candidates who have qualified JEE Mains or JEE Advanced can apply for the counselling process and also they should have at least 75% in their respective board or under the top 20 percentile.