I like part of all 3 shows. Regarding the "judges", on AI they are just that, and are not supposed to be mentors or cheerleaders, so I don't care for many of their comments. At least Simon was honest with them for the most part and offered some constructive criticism.
Although there was some good music at times on X Factor (which is what I hope for when I watch these shows), my problem with it is that Simon et al are supposed to be mentors, but go too far in the direction of bashing other mentor's contestants which ruins the feedback part of the shows.
The team mentors on The Voice seem to strike a better balance, but there are some other flaws in the show, such as the battle rounds. They end up pairing up some good singers which decreases the chance of them having the best ones continue on.
In the latter stages of the competitions, I think it's fairer to keep the best singers, not just the best in each team.