I believe Sentry would win this in an unconventional fashion really.
He would bathe RKT in so much fabulous light that RKT would be paralyzed in a Fabio like pose just turning his head left and right to really let that silky hair shine come out.....................
Then Void would come and since RKT would be Fabio'd and ridiculously stuck on his fabulous hair would lose............
LOL yeah RKT cuz there is very very lightly chance Sentry could be Odin and RKT is much stronger then his father.