Ah, that's a shame about Fairy Tail, but I suppose that's the case with most long running series. One Piece has so far averted that, though I've read a few people hating on the show post-timeskip. One Piece has forced me to change my tune on subs, which were never negative but I never gave them a chance before due to some bad past instances.
Yeah, I had to switch over two episodes ago. Luckily I'm already familiar with the voice cast since I've watched a two of the movies. I think Eric Vale & Luci Christian do a better job as Sanji & Nami respectively, but I think the Seiyuu of Luffy is better than Colleen Clinkenbeard. Everyone else in the crew (though I haven't heard the shipwright yet [not spoiling who it is even though it's hard not to know if you're slightly familiar with the series]) are pretty equal in both languages. I will say that John Swasey was terrible as Crocodile in the dub, but his Seiyuu was phenomenal.
I've heard very little about Claymore, so that's nice. I have two hundred animes on my planned to watch list, so I doubt I'll be getting to it anytime soon.