My favorite PvP to organize is AB - people can bring anything they want really, and in fact its a great testing ground for new builds. The only real drawback (as everyone knows) is the wait time, but I tend to just minimize GW, cue up some music, check my email, chat on TS, etc. while waiting. So personally waiting for AB is no big deal for me.
When I'm not organizing but just playing, I do prefer HA. It is the greatest challenge as far as the builds, both personal and team builds, and strategy.
And definitely the greatest reward for winning - getting ranked is just awesome. Its biggest drawback is that the highly competitive people who enjoy and are good at HA tend to be hard to work with. No offense to anyone in particular.
Also everyone can end up standing around all night without playing when we end up with too few people, or too much inflexibility with builds. Its even worse for the PvP organizer, because that person doesn't only not get to play, but also wastes a bunch of time spamming Alliance for players, working with peoples builds, etc. Not to mention putting up with all the whining and complaining.
When I'm organizing HA I can't have music going or anything else that might distract me, I have to work double-time to keep up with everything that's going on, and its hard work. But again, if someone else is doing that and I'm just playing, I really do love HA.
there is a group of experienced and/or "willing to be flexible and patient" players on hand