I'm playing a warlord and it's really fun ... IF you have an ally adjacent to the target your fighting.

Generally speaking this isn't hard to achieve provided you delay your turn until after your ally chooses to act. Once you have an ally attacking the target with you, you kick butt. It's really easy to get flanking with
Wolf Pack Tactics.
Furious Smash is fun to use against those frail, low Fort Skirmisher monsters

.
Commander's Strike and
Hammer and Anvil nice if you're fighting with a Str primary character. Becuase I'm human and have the Action Surge feat, I'm also pretty good when it comes to using my dailies (
Stand the Fallen and
Bastion of Defense).
Aid the Injured rounds out my healing abilities - I'm the group's primary healer.
So I have a good time, but I really need allies helping me to be most effective. A rogue kinda sort of needs that with regards to achieving combat advantage, but at least the rogue can use Stealth to get CA and then do a ranged attack. But in general I find that I'm able to get enough help from friends to do a good job most of the time.
So it boils down to what your preference is as a player - do you want to look awesome because you tend to do the most damage, or do you want to look awesome because you help others be awesome? If you're still not sure, another consideration is what the group needs. If noone is playing a Leader character, I'd choose warlord. If noone is playing a Striker, the rogue may be a better choice. Do you know what the other players are playing? If so, let us know and we can brainstorm some ideas with you.