The best normal starters are as followed:
Grookey, Scorbunny, Bulbasaur, Charmander & Froakie.
For Custom starters:
Honedge, Gligar, Eevee, Vulpix (Can't remember any more important ones)
Most of these pokemon require their Hidden Ability to be good. Else they really struggle due to terrible abilities (Torrent, Blaze & Overgrow). Don't worry too much about it. It's better to get a starter you like instead of one you don't like ^^