If you get a real nice recapped 1200, it will be a better value especially with WHDLoad.
If you want a bone stock system, the 500 will be the least expensive and the vast majority of games will run fine on it.
Most if not all educational games are ECS/OCS, if you ever plan on them for the kids also.
I echo the above on the 2000. If you want a kid friendly machine the 2000 is about indestructible and they are real cheap to acquire.
Both the 1200 and 2000 could easily use different media to get away from floppy switching.
Good luck!
