Of course Ditto XP, but if I couldn't cheat, it would be Absol. Or maybe Rapidash, or Charizard, or Houndoom, or Ninetails. Wow, all fire XP!
If I were water...
Gyrados, or Lapras, or Lanturn.
If I were grass...
Meganium, or Tropius, or... wait, that's it!
If I were steel...
Metagross or Steelix
If were normal...
Zigzagoon or Tauros
If were psychic...
Espeon, or Claydol, or Gardevoir
If I were flying...
Swellow or Altaria
If I were ghost...
Misdreavus or Bannete
If I were fighting...
Machoke
If I were electric...
Raichu or Manetric
If I were dragon...
Dragonite, or Salamance, or Flygon
If I were rock...
Umm... Aggron or Tyranitar
If I were ground...
Sandslash
If I were poison...
Seviper
Wow, that unnecisarily (SP?) long. Hopefully I got everything!