the HP is not much more on the 6.2's because the compression is lower. So, in theory, the 6.2's make more HP and should be more reliable. I'd take the boat either way though. both are solid engines and run well in the 280.
Please also note there were different 5.7's, there is a 350 Mag (300hp) and a 5.7 mpi (260 HP). Merc phased out the old 260hp version but just beware of that while looking used. The 5.7's run great in that boat too, just a bit slower.