Swapped from 25 to 10 man with cata and never regretted it. I felt more connected, more fun (on 25m there was always a bunch of slackers we had to carry since Vanilla to fill the raid), less stress (internet/pc problems reduced by factor 2.5 statistically) and we still had to work our asses of for the kills. It's not like either side gets free loot but both just have different problems to handle inside and outside the raid. Only real downside? It felt slightly less epic than coordinating 25/40 man, but that's about it.
-> whoever get's first should be treated like that