Hermann's, just because, as a rule, they are the most "interactive"...every Russian or Greek I've ever owned has taken anywhere from a week to a month before they're tame enough to eat out of your hand...with Hermann's, otoh, it's more like as soon as they see you've got something they want!
What's not to love!
Which is not to say that any of the three doesn't make an excellent choice...
I keep (and breed) Eastern Hermann's the most common of the subspecies, Ibera Greeks which are the Northern Mediterranean species (There are also Greeks from the Middle East and North Africa) and Russian tortoises. I like them all for different reasons. Hermann's are definitely the most "personable" of the three species that you mention, hands down. I like Hermann's because they are typically unaffraid of anything, constantly curious and do very well in a variety of environments. I also prefer their appearance over the other two species. Russian tortoises are probably second on my list of the three. They are like small, round bulldozers! They too can are very hardy once adjusted to new living conditions but do seem to take a while longer to "come out of their shell (pun intended). While I do like them very much, none that I have ever had came close to Hermann's in the personality or curiousity department. They aren't as colorful either. But I just really like their tough appearance and actions. I'm not much on Middle Eastern or North African Greeks here where I live in the Northeast because they simply do not do well outdoors in my area. I prefer that all of my tortoises be outdoors absolutely as much as possible. But the Northern Mediterranean Ibera Greeks, do very well in a variety of climates, much like the Hermann's. They aren't much on brilliant colors or contrast once they get older. Personality wise they seem to be hit or miss. Some of mine nearly rival the Hermann's but the majority of them just sit and watch whats going on with very little curious interest. They seem more content to just eat and lay around in the sun. Some of them, even after years of being here, still scramble for cover when I come around.
All in all though I think that any of the three are good choices. Russian tortoises can easily be found at very reasonable prices on Craigslist and some other sites. I always advocate buying from a breeder or getting one from an individual who no longer wants it over purchasing from a pet shop.