Is floating or sliding better in this case of round 2 and moving for round 3?

Hey Arun,
You have to understand what floating and sliding options do. If you select floating option, then you can get any of the preferences you have filled above the one you have got in the current round. On the other hand, sliding ensures that the college you have been allotted in the current round doesn't change. Only the branch can change, in case only, if you have filled other branches as higher preference. So, as you mentioned you have filled the same college in higher preferences, hence you will be assigned the same college, no matter what you choose - sliding or floating. In case, if you are satisfied with the college and want your branch upgraded, you can go with the sliding option.
I hope its clear now!