I found 25 mans to be far too demanding overall, unless the group was predominantly a bunch of friends. In general, guild urn 25 mans suffered horrible downtime, botched coordination, and the occasional rager in vent/teamspeak/etc. In general I prefer 10 mans, where you can always tell who's helping, who's holding the group back, develop teamwork skills faster, etc.
Pretty much the only fun I had in 25 mans was during the WoTLK expansion, with ICC. It wasn't a guild run, and instead included friends from various guilds that weren't large enough to do 25 mans effectively. We had been playing together for years in terms of instance/dungeon runs, so everyone was familiar with each other and there were no issues with loot or rage.
On a side note, raids always seemed to go better if a couple people were parents, or older players. Moms especially seemed to effortlessly get people to chill the fuck out.