700c will be what you want to run on this frame. As others have mentioned how wide you can go on tires may be an issue (23 or 25c should fit). For the rear because it's 120mm spaced currently it won't fit more modern wheels, but a good shop can spread the rear to the standard 130mm if you want to go that way (allowing you to run modern cassettes/gears). For some ideas on what people have done for non classic check out:
The New Classic Rigs and Rides Thread 1.1
The mafac racers have good wheel/tire clearance.