really, an argument could be made for any starter.
Venusaur is more or less the metric by which all other Chlorophyll Pokemon are judged
Charizard has Bonkers damage whn properly supported by a team
Blastoise is a fantastic doubles support, and in gen 8 will arguably be the best Shell Smash user, even moreso if it can Mega Evolve
Meganium has a fantastic early game, learning Razor Leaf Super early, and is amazing at keeping the party alive
Feraligatr has Sheer Force, so overwhelming amounts of physical damage
Typhlosion is quite similar to