Personally, mine would be;
Kanto:
Charmander 90% of the time
Squirtle 10% of the time
Johto:
Totodial 80% of the time
Cyndaquil 20% of the time
Hoenn:
Treeko and Mudkip on a 50/50 basis (depends on how I'm feeling)
Sinnoh:
Chimchar 75% of the time
Turtwig 25% of the time
Unova:
Snivy 80% of the time
Oshawott 20% of the time