My answer would be either none of them, or all of them except human. You can be human and make just about any character concept work. For the other races, the moment you start looking at something non-cliche, you start running into problems. Try making a Tiefling Fighter, Eladrin Paladin, Dwarf Rogue, Halfling Cleric, Dragonborn Wizard, Elf Warlord, or Half-elf Ranger, and you'll see what I mean.
It's difficult to ignore the difference in competance between a Halfling Cleric and a Dwarf Cleric, or between a Halfling Rogue and a Dwarf Rogue.
I think this is one of the few steps back from 3.x, where you could take a Halfling Cleric, give him a level of Rogue, and be an excellent tumbling combat healer. Or you could give the Dwarf Rogue a level of Fighter for a very survivable flanker, and a great dungeoneer.
In 4.0, in order not be outdone by the other characters, you pretty much have to play one of the few "recommended" race/class/stat combinations.