Two thousand and ten.
Two reasons:
a) The films 2001 and 2010 Space Odysseys were never called twenty oh one and twenty ten, so even though it looks like a break in tradition, (ie 1960 being nineteen sixty etc), it's not because before we ever reached the millenium people weren't saying twenty whatever for the years ahead, they always said two thousand and xxx etc.
b) Twenty ten etc just sounds lazy to me, also it's far too American "sounding" for my liking.
So basically Two thousand and ten because traditionally/historically that's how us brits have always pronounced the post millenium years, (before the millenium actually occured that is), and I hate change for the sake of changes sake and pointless re-invention/renaming has always bugged the hell out of me