My vote goes to Piplup. Learns Bubblebeam before Brock, the strongest stab move among starters at that level and Aqua Jet. If you are using Rare Candies, or can cheese it by switch training, you can keep cancelling the evolution and Piplup will learn Grass Knot at level 25 and then can evolve to Prinplup for Misty. You’ll need a strong team of 5 around it though to keep it first stage for that long however. Then Water/Steel is great typing and has great Special Defense. It’s not one that gets a mega evolution or people go crazy over but you are guaranteed several other starters through the game. Generally you are relying on the starter you initially pick to get you through the early early game. A small argument can be made for Turtwig as it’s a grass type for the first two gyms and can have the starting ability Self-Sufficent, which is built in leftovers. However you do need to face Faulkner and all of Misty’s pokemon have Ice coverage


Turtwig has nice ability "Self Sufficient", pretty much free built in leftovers