From a hardiness perspective Herman's and Marginated would be equal (both, like Russian's, are almost bulletproof when the husbandry is correct) the Greek's would be last only because there are so many types of Greek's. Testudo Ibera (Greek) from Turkey are very hardy, the equal of Herman's and Marginated. Testudo Graeca Graeca and all the subspecies thereof are more demanding. I have two subspecies (Graeca Terrestris and Graeca Soussensis) and they are more finicky that Ibera.
Size wise Herman's and Ibera will end up being 6-8" for males and up to 10" for females. Marginated are the largest tort of your choices (although some rare Graeca subspecies get up to 12 "
getting up to 11-13".
Marginated are less common, so if you have the room they'd be my choice. They are also the most distinctive because of the flared marginal scutes. Downside is they get big and need space. Housing them indoors year round is not a good option. One adult would need a minimum 9' x 9' pen. They will also cost a bit more than Herman's or Ibera's.
Herman's are a great smaller tortoise, equal to Russian's. Their upside is, unlike Russian's, they aren't a minature Sulcata (read: they don't dig long burrows). They hide under plants and bushes as opposed to digging a burrow. No real downside since they stay small and can adapt to almost any environment. Either variant of Herman's (Hermanii - Western race or Boettgeri- Eastern race) is a good choice, although I'm partial to the Boettgeri and IMHO they are a little more hardy due to a more northern natural range.
If you go the Greek route, go Ibera. They are the same as Herman's in almost every respect.
Good luck.
