I like Ho-oh, Latios, Rayquaza, Kyogre, Suicune, Raikou, Zapdos, Mew, and Celebi. I like Ho-oh, Latios, Suicune, and Zapdos especially.
I get upset when I see the tier-I legendaries (Kyogre, Groudon, Rayquaza, Ho-oh, Lugia, Mewtwo, Deoxys, both Latis with Soul Dew) being used in competitive battles. They take a lot of skill to capture, but demonstrate little skill in raising monsters and strategy. I was very disappointed by what I saw in the JAA event in San Jose; the finalists in both age divisions all used at least 2 of the mentioned legendaries. I hope that somewhere out there, there was, or will be, at least one 1st place team that doesn't use any legendaries whatsoever. They get my full support.
This isn't to say, that these monsters are permanently broken. It would take some time to contemplate, but I think the best solution is to set a level restriction for Lv. 100 matches (Kyogre can be no higher than Lv. 85, Ho-oh can be no higher than Lv. 90, etc). That way, the spirit of the game is kept intact, and there is a slightly wider selection of monsters to choose from. Kyogre and Groudon are desireable for their auto-weather, the only acceptable monster with auto-weather right now is Tyranitar, which causes a Sandstorm.
Wobbuffet with Leftovers and possibly Ditto with Metal Powder should have restrictions for different reasons. Wobbuffet vs. Wobbuffet with both holding Leftovers results in an inconclusive, never-ending match, since Leftovers heals more damage than Struggle inflicts. Ditto with Metal Powder can Transform into Shuckle. Shuckle has bad HP, but Ditto doesn't. Ditto copies all stats, except for HP. Combine Shuckle's defense with Ditto's larger HP and Metal Powder, and you have a tank.