@.access:
Feraligatr and Serperior were definitely the hardest starters to handle from those I picked. Serperior is just no good as a starter (non-offensive pokémon are generally bad outside of pvp and Serperior without its HA has almost no offensive presence) and Feraligatr back in GS would only learn two water moves: Water Gun back in its Totodile days and then Hydro Pump at level 58. And it was not like the rest of its move set was any better, I remember how frustrated I was waiting for it to finally learn a useful move and it never happening (remember back then TM were one-time only, which in my case meant "never use those. Except to give Psychic to Butterfree").
Hopefully I liked both enough to struggle through, but the memories are still here.
I remember playing Silver and just wrecking everything with my feraligatr. It knew Bite, Surf, Slash, and probably strength, though I'm not sure on that one. It was 30-40 levels higher than everything else and I ended up fighting high level tentacruels that I caught with a super rod outside of Vermillion city to get it to 100. Good times.