Thanks for the idea, Ghostey! I feel like I'm in a good position to look at this question from all sides, at least from the perspective of a raiding guild. Between the two classes I've played most in raids, I've covered every possible role.
In vanilla WoW I played a hunter. Looking back, I feel like that was the perfect class to play back then for a guild leader. In our raids, hunters handled the tricky trash pulls (original, nonscaling, 13-damage Rank 1 Arcane Shot for the win), and most of them back then were tricky. We even made some boss pulls (Eyes of the Beast fooled Baron Geddon every time -- that guy really hates animals). I wasn't leading these raids, mind you, but it did allow me to set the pace to what I felt our raid team could handle.
The other great advantage of being a ranged DPS -- that still applies today -- is that it allows you to survey the team effectively. You can see who's out of position and who's reacting slowly to changing fight conditions. You can see when the tanks are slow to pick up adds and when healers are moving for no good reason when they should be spamming their biggest heals.
It definitely gives you the best vantage point of the battle. You can make mental notes of these mistakes. If they happen frequently, you can have a private conversation with the player to help them improve their reaction times. (Or you can mention it to your raid leaders, if they handle such conversations exclusively.)
In TBC, I played a paladin as both a tank and a healer. A tank is a great class to play as a raid leader, because it allows you to set the pace of the run. Plus, most raids live or die by how heads-up their tanks are. If you're one of your guild's better players, you'll be a big part of your guild's success in a tanking role.
But as a guild leader who's looking for potential issues, you don't have time to notice much about what's going on around you. Not to mention, your field of view is quite limited. You're staring at some giant monster's legs/pelvic area 90% of the time. Even with your camera fully zoomed out, you can't see everything. You'll have to rely on other officers to help you identify potential problems.
Healers, like ranged DPS, also have a great view of the action. However, unlike the DPS classes, healers spend the whole fight watching health bars rather than what's happening around them. You'll certainly notice if someone is standing in fire as their health plummets, or when someone lets a boss ability instagib them. You'll also have a better sense of whether your other healers are doing enough to let the raid succeed. But, you won't be as able to catch the subtle issues that your raidmates may be experiencing.
Finally, in Wrath, I play my paladin mainly as a Retribution spec, filling in as a healer when needed. Melee DPS, like tanks, have a limited visual range. I find myself wishing sometimes that I played a ranged class, to give myself a better view of what's happening, particularly when we're learning a new encounter. But I don't find it to be an enormous crutch, either.
Part of it has to do with the fact that I know my raid team pretty well at this point in the expansion. I know their strengths and weaknesses, so I know what to look for. If you don't know these things yet, then playing a melee class will slow down, to some degree, your acquisition of this knowledge.
Of course, the most important thing is to encourage an environment of honesty and communication, so players will admit when they're having a problem. Then you can all talk about how to help them. That way, you won't have to do so much observation and critique.
Ideally, you trust everyone on the team to do their job well and to raise issues when they crop up. In that case, it really doesn't matter what you play.
But many guild leaders don't find themselves in this ideal situation very often. In those cases, I would have to say that a ranged DPS class is your best option.
Keep in mind, however, that if you are one of the better players in the guild (and in most raiding guilds I'd say this is the case), then you will be limiting your contribution to the team's success. It has become less true than it was before every raid boss had an enrage timer, but even so tanks and healers are still the roles that decide, more often than not, whether you will win any given encounter.
In terms of specific classes, I think the Paladin class is overall the strongest for unique raid support. I may be biased, but I don't think anyone can argue it. Divine Sacrifice, Aura Mastery, Hand of Protection, Hand of Freedom, and Lay on Hands are all unique support abilities whose usage can make or break an attempt. And these are just baseline abilities or 11-point talents. Even Hand of Salvation can be important, for instance, when trying to beat Hodir's hard mode timer. Judgments are unique debuffs that increase the survivability and longevity of your tanks and damage dealers. A raid without a paladin is losing out on a lot of utility, although there are very few raids that are missing one these days...
Druids would come second with Rebirth, Innervate, and Tranquility. As an aside, it's a shame to me that druids aren't more effective when switching forms mid-battle. Not to say they should be equally effective regardless of spec and gear, but if there's one class that could be played as a true hybrid, given the nature of its mechanics, it's the Druid class. That's one thing I'd love to see change in Cataclysm (although it would probably be unbalanced for Blizzard's precious arenas). Back in vanilla WoW, when Druid gear was such a laughable mishmash of stats, it was easier for Druids to play the class this way in an emergency. Of course, it also gimped them terribly in the role they actually wanted to play most of the time.
So, if you're looking to play a stronger part in beating encounters, those two classes have the most to offer regardless of your role. I'm not saying other classes are worthless by any means, but most of their active utility is shared by other classes.
I will also add this caveat: We guild leaders endure a lot of stress and pressure and worry. If it makes you happy to play your chosen class, regardless of what it is, then stick with it. I don't think the meager benefits of playing one role versus another outweigh your own fun. We deal with enough unfun things. Your class definitely shouldn't be one of them.
What do you think? Do you find your class to have any particular advantages or disadvantages for you as a guild leader or officer?