I say Machop. The only reason the Psychic one wasn't Abra is because Alakazam won't be in this set. The other 5 are all the popular Basics from the Base/Jungle days.
Charmander
Squirtle
Bulbasaur
Pikachu
Mr. Mime
Machop
If its not Machop then, it probably will be Sandshrew. Hitmonchan is not really an option cause (a)its bigger than the other 5 and (b)we just got a Hitmonchan. I spose it would be Diglet, Cubone, Mankey or Rhydon but: Mankey has never been popular and probably wouldn't be recognized by the younger crowd. Rhydon would look terrible as a Ditto and again doesn't fit the mold. Cubone has a skull on its head so we wouldn't get that feel of a Ditto. It wouldn't fit the mold if Ditto Form Changed into Diglet. What I'm trying to say is that its either Machop or Sandshrew, 99% guranteed its Machop.
This is all very nice because it ensures that we won't have another "Base" set to overshadow FRLG. Simple math tells you that there is not enough room in cards #1-2 to fit Blastoise, Charizard & Crobat. If they're ex or if the "renditions" on PokemonZeo are wrong, all bets are off.