Thanks Shivangi for replying, this time in first round counselling they have called candidates upto 1240 OBC rank as total number of OBC seats in AIIMS has increased from 217 to 313 this year out of 1207 seats available. I am in the hope as the rank difference of 1240 and mine i.e 1520 is not that much may be they can call me in 3rd round or mop up round because students having better rank than me may less prefer the newly opened AIIMS.

If you compare your category rank with 520 then the difference is 1000 and 81 new seats reserved for OBC which makes total of 324(old seats 243) it means you'll be against 324 seats. You'll be finding ot difficult but if I was in your place, I would be doing same thing as you(waiting till the last round of counselling) as your logic for less preferring by better rankers is true.GOOD LUCK.