Favorite: Totodile. Best reptilian Pokemon design of all time, imo. Plus Feraligatr is a monster. Plus Wooper is my favorite and I must always have one in my G/HG team. Along with Feraligatr it can be ensured all the water HMs are evenly distributed.
Least: Tepig. Tepig itself is cute enough but Emboar is awful looking, and both fire/fighting starters before it are so much better-designed and just as strong, if not stronger. And if you have a worse design than the Chimchar line, you have some very serious problems.
I don't understand all the Mudkip hate. I tend to favor water starters, though. But Swampert's electric immunity? Fuck yo' Dragonite's Thunder; Blizzard, bitch! xD
Honestly I just caught a Torkoal and it, alongside my Swalot, murdered the face right off that Sceptile. Problem solved.