Squirtle hands is the best start in Pokemon Blue-Red, mainly because of the abundance of ground in the Pokemon games. Its attack stats are equal with Bulbasaur and with the exception of speed, the swing and Grass Fire-Poison counterparts on all counts. He learned his last and most powerful technical level 42, so it's a good idea to wait for developments in Wartortle until the last possible moment.
Use Squirtle against fire, soil and Rock opponents for the best, but it can hold its own against the types of ice (at least on the defensive side of things). The lesson to HM 03 - Surf is a no-head, but you may also want to consider adding non-water moves as Blizzard Dig and give it a wider range. In an emergency, Dig Squirtle could help get at least a touchdown on an opponent-type power. Squirtle does not last long in a battle against the Thunder or Grass Pokemon. Thunder Electric or any other attacks usually hit it at once.