I've always thought 25m raids were MUCH MUCH MUCH easier, seems to be a slight buffer in most encounters that lets a healer or dps screw up, with much less penalty than a 10m.
10mans in 25man gear are quite easy - 10 mans in beginning raid gear however...
25mans are MUCH easier.
That's why all these guilds are staying 25m (Cuz its easier, not cuz its OMG HARDCORE)
Spoken like someone who's never done hard-mode content. I'm not going to bother going into any more detail. You have zero experience, therefore your opinion counts for just as much.