>>4651
To begin, I'd suggest you go with the first ReBirth. If you enjoy it, you may be hooked enough to go and try the two others. If not, the story is a stand alone so you won't be too invested into it.
As for the best, it depends from one's favorite to another, but VII is often one of the most appreciated. Don't go on it before doing at least ReBirth 2 and 3, though.
Anime is basically a fast recap of the three ReBirths, with small variations that makes it enjoyable on its own, but watching it means you'll be spoiled for three games at once, which can be a problem if you enjoy the story and characters.