Man, I don't like compulsory pokemon - starters, forced legendaries, etc. Usually just box them, after getting a 'mon that resonates with me.
Ultra Moon had Alolan Muk as my ace, but I'll usually go for psychics, dark-types, poison-types, etc, and try to feed them battles when I can, so they don't fall behind.
Starters are paradoxically 'special', in that you're one of the few people in the game that have them, but from a meta-perspective, every little child is going to be rocking one of the three, and they don't really convey the user's personality because of this - they're very boring picks.
Will usually forgo unique units for generic ones, in other RPGs as well, if given the choice.