Feraligatr checks a lot of boxes as your Z-A starter (especially since the other options are all pretty slow)
rest is up to what you like but I'd try to make an all-Mega Evolution team if possible
tbh i dropped all the starters of Z-A
Been rotating my team a lot between Garchomp, Gardevoir, Greninja, Excadrill, Froslass, Charizard (Mega Y), Eelektross, Swampert, Lucario (Physical), Raichu (in prep for Raichu Y), Gengar and Absol (in prep for Absol Z)
Need to get the mega stones for Greninja and Swampert.
I've yet to do a single ranked battle, only been playing it for the last month to finish the story as quick as possible. Even have a Annihilape that i EV trained in Scarlet for easily dispatching rogue battles.
All i gotta do is get the team to Level 100 and EV train the team