It all depends on just one thing : The branch you need.

• Almost all branches of all IITs end up at approx 15000 ranks.
• But then also so many seats remain vacant there because so many students leave their seats blank and move to NITs and IIITs. The reason is quite simple, they didn't get their preferred branch.
• My cousin scored an AIR nearly 6000, he could get into IIT indore, or lower IITs with his preferrwd branch. But, he left his JEE ADV seat and got admitted to IIIT, Hyderabad with EE branch. It is really better if we neglect the future changes.
• While some scored around 3000–4000 ranks and are now in IIT Kharagpur.
• One of my friends is now in IIT Guwahati with AIR around 11000.