people just like piplup because it's a penguin...and everyone (excluding me and a lot of others. penguin h8ers representt) loooves penguins after March of the Penguins, Happy Feet, and Surf's Up were made. wtfuxx0r?
Since Empoleon is Water/Steel type, it gains a weakness against Fighting, Ground, and loses it's resistance to Fire but it gets an immunity to poison. It does have sweet special atk and defense skillz, but like the worst speed ever.
Squirtle is good because its higher defense and spec. def powah especially as Blastoise...but has sucky speed.
Tododile is good because of high attack and defense, but it has low Sp. Atk and Sp. Def and rly sucky speed. BUT it gets to its final form the fastest. Lv 30.
Mudkip is good because Marshtomp has an immunity to Electric....but is even weaker against Grass...it has very high attack, but the most horrible speed evah.
hmm...i kinda like speed, so I'm definitely not saying Mudkip or Piplup. Croconaw does become Feraligatr at lv 30 while Wartortle evolves @ lv 36. It really comes down to a preference of high defenses, or high normal attack and defense. I'd go w/ Squirtle. 1st gen all teh way!!!