I think if you've got a reasonably new motor you should stick to the manufactures oil. If anything goes wrong with the motor and you need warranty assistance I think it would help the case.
They all probably come from the same place anyway. BP, Castrol ,Mobil etc, probably make the oil for Quicksilver , Evinrude. I cant see Evinrude etc in the oil game, I think there just branded that way. I dont know that for sure, but these marine companies make outboards not oil. I dont think there is any difference in quality in my experience, not that youd notice anyway. I use Mobil mostly.
Cheers