hella will give you more gains.osta has less sides.osta is a better compound imo because it is SO versatile.. can use in pct .. in bridge ..etc etc.Which make it a ground breaking coumpound.i like hella but im more a fan of osta because of the very low sides and the versatility.I guess from a pure size gaining angle, you would wanna use hella though.
If it was pure size i was after, there are better options then both to be honest though