There is so much I could say about Dwarfies I just love them so much. I will try and keep it short and sweet though so that you dont have to read pages. ^_^
Robos - Take a long time to tame, need a lot of attention to get them used to you but are more than worth it if you succeed (and even if you dont) They are cute, fun, fast and - from my experience - get along with others of their kind much better than the other dwarf breeds. Of course there are always exceptions
(Ps these are my favourite dwarfies ^_^ I own 2, soon to be 4, robos)
Russians/Hybrids - Friendly, easy to tame in comparison to robos, can be very cuddly or quite fiesty, occasionally nippy at first, great personalities, better for first time dwarf owners as they can be handled outside of the cage quite easily and arent as squirmy or as fast as robos. I have 1 hybrid and she is absolutly lovely but very feisty.
Winter whites - Very very loving. Although I'd recommend only getting one WW unless you are prepared for the very likely chance of a pair fighting and having to be separated at some point in their lives. They are, I find, the most social with humans out of the dwarfies. My WW loves to cuddle with me or sit on the shelf in her cage chattering to me. She will respond to me if I speak to her and sleep by my head some nights 'cooing' at me when I start to drift off :L (Not a great help when youre tired) All in all though they are beautiful and very sweet.
Ive yet to own a Chinese (although they are not dwarfs a lot of people percieve them to be so I thought I best mention them) My cousin has owned two - who had to be separated and this is apparently not all that uncommon with chinese but she loves them and they are very friendly and sweet natured although they can be very shy and sometimes hard to tame.