I had the same issue with flip-tops. I gave up on them and just went to kegging. I'm glad I kept a few of the flip-tops, though, because they're great when filling with already carbonated beer from the keg.
Bottom line, they don't make them like they used to. I think the problem comes when you're installing the wire bale. If you aren't gentle enough, the bale gets a little loose and doesn't pull tightly enough on the seal to make it stand up to the pressure of the natural carbonation process. But they still work fine for keeping cold carbonated beer sealed off, if that makes sense.
If you want to give your bottles another chance, you could try replacing the bale assemblies and make sure you get them installed properly on the first try and verrrry gently. I'm pretty convinced that this is the problem, because I noticed that the percentage of bottles that wouldn't carbonate correlated pretty closely to the percentage of bottles where I had trouble installing the bale -- either because I installed it "backwards" the first time (where the flip is on the wrong side after you click the bale in, and you have to force the flip to the other side) or because it kept slipping and I had to re-do it several times (weakening the bale).