Their personalities do vary, it's true. And some hamsters can be a bit more used to people/tamer. But species characteristics are also different. I will admit to not knowing much about Russian Dwarf hamsters, having never had one, except that they are small!
I've had Syrians and Robos and love both but very different types of hamsters to keep and Robos are known as "watch" pets a lot of the time. Which I agree with. Some people do tame robos and have out of cage time, but they are so incredibly fast. And generally the most fearing of species (being prey and so tiny). They are great to watch and talk to (if you see them!). But I find there is nothing like a Syrian for handling. Even shy syrians are great to handle and big and lovable. More active syrians are great to interact with (and keep you on your toes). And generally they're recommended as a first pet hamster. A kind of learning curve!
I also think it's great you're thinking of the ones that most need adopting. On the other hand I wouldn't want to think of you feeling disappointed at a first experience. My ideal "mix" is to have both a Syrian and a Robo
. When I had two Syrians that was nice but found it hard to give both of them enough attention regularly.
Our first robo I adopted (from an unwanted litter) and he was already freaked out by his early experiences with inexperienced owners. He literally was a watch and talk to pet. I was very fond of him but it was frustrating not being able to handle him. I did manage to eventually - a tiny bit, when he got a bit older, but then he got cancer. Sadly.