Consider the time it takes to level from 1-70, or 55-70, you could always just try both and see which you enjoy more.
Deathknights have more self-healing, control, ranged abilities, More 'smallish' cooldowns, ie; Anti-magic shell, Can put out huge burst as Frost or blood, unholy is a bit more sustained, Aswell as a nice mix of magical abilities to knock down high-armor targets.
Warriors are rather gimped in this bracket, lack of Heroic leap, second closer, colossus smash, etc. I'm not expert on warriors, but expect they'd always need escorts/healers to do decently, Arms' can still put out a lot of damage, and protection is very mobile, and has a lot of control. No idea how fury fares.
Overall, Deathknights are currently in better shape in the bracket, but play whichever you enjoy more.