I've never had female rats- I used to have female mice, and have a couple of male rats now, and they're great. They do have massive balls, which does freak people out a bit, but as their owner you get used to it!
They do smell if I leave cleaning their cage for longer than a week, but generally they're very clean, lovely boys! They fight, but it's mainly just play fighting I think- they've never made each other bleed.
They're definitely awesome pets though! =)