Any of those are great when it comes to being friendly and easy to care for. None of them have special temp or humidity requirements, just give them an UTH and make sure your house is relatively warm, and you're good to go. From what I've heard, they're all pretty laid back snakes, although of all of them I've heard the most about hogs being skittish sometimes. Rosy boas and the roughscaled sand boas can grow to be slightly larger than the other two, but they're still small at 3-4 feet.

I really like sand boas, but I guess the main problem I have with them is that you never really see them. Now, I've never owned one myself, but when I worked at Petsmart we had one there, and he was always buried under his sand. Really cute little guys once you found them and dug them up, but I personally like to be able to look in and see my snakes, even if it's only a tiny part of them when they're curled up in their hides. I might get one at some point, but I went with a rosy boa myself

It's really up to you though. Since you've been doing your research, I'm sure any one of them would be great!