Hi there I have all varieties of dwarf hamster at the moment; chinese, roborovski, campbells and winter white. Winter whites are my favourite and the only type of dwarf hamster i breed currently but i'm going to try not to be too biast towards them when answering your questions
Which is the best one to tame? As long as you get the hamster(s) from a good breeder and handle it regularly enough any hamster is easier to tame. Out of the dwarfs winter whites and robos are better i feel for handling although winter whites are a little nippy sometimes (if you have the smell of food on your hands) robos are very very fast (like grease lightening is the best description i've heard!
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Which is the one which bites the least I'd say robo's although that doesn't mean to say you'll never be bitten from a robo.
Which one can you keep in pairs? Past experience of robos didn't end well with them being in groups they all fought between each other, winter whites do well as pairs and campbells do well in pairs or groups. Chinese females can be difficult to keep in pairs i'm not too sure about the boys.
Hope this helps you, ever need any more advice you know where we are!!