I voted Rogue, but I will probably be DMing.
I like the Rogue because:
"I poke you here, you move over there."
"Ah, a chink in your armor, to bad."
"So what if they call me a backstabber."
"You can't keep up with me can you?"
In other words, they hit hard, move targets around, can attack reflex or will defence and can move around really well on the battlefield. In addition they can sneak and bluff with the best.
One of my playtesters first played the Wizard and then the Paladin from the pregen characters.
Him, after the first session: "I am going to play the wizard".
Me, before the second session: "You have to try another character."
Him: "Ok, I think I will try the Paladin"
Him after the second session: "I am going to play the Paladin"
The only class I didn't get impressed by where the Ranger and Warlock. The synergy with the rest of the party was quite low. If you compare them to the third striker, the Rogue you will notice that the Rogue will make it much easier for the party to set up flanking and that the Rogue will soak a bit of damage that otherwise would have targeted the Fighter/Paladin. In addition the rogue has some crowd control abilities from the encounter/daily powers (move enemies 1+ squares).