So on this Topic Matt. There are many diffrent opinons I am sure so here is mine.
First I will explain both side.
25 man raiding.With 25 man raiding it takes more communicaton,Effort and Trust.
Some fights you have depend on 24 other people to do there job instead of 9 others in 10 man. With a big roster you have to find ways to close the learning curve. Which usuualy is quite big since you are taking on 25 man. And with so many people to depend on it can be rough. But in the end I feel 25 mans are harder but completion of 25 man content I still feel is more relevant then 10 man. You down 10 man gg. But 25 man its another level of play style. Its harder and it takes more.
2 10 mans on the other hand have there pros and cons too.
First most likely you will see more progression. Its easier to find out when someone messes up and what not. And most strategys are much easier with only 10 people. The communciaton still has to be there but not as much. You have team A and team B. I was an officer in this type of guild and it was very successful. It does drive healthy competion with in the guild. But as below it can drive jealousy and what not between the groups. Which usuualy can be setteled by meetings and time for both groups too come together we did a monthly meeting to make sure we were all on the same page. But it also allows you too share best pracitces and what helps each group achieve kills. Group A can give Group B tips and the other way around. And it much easier to manage and raid dates some times are easy to manage because you only need to accomodate those 10 people in your squad instead of the whole 25.
I have much more on this topic and will go in detail mabey in mumble and post another topic on it.
But I really loved running 2 10 mans when I was an officer. But I enjoy 25 mans much better. It is more headaches and as each xpac comes gets tougher. I still really enjoy being the best and downing content in a harder more challenging fashion. Compared to 10 mans I will take 25 man because the way I feel inside when we do achieve a kill you share it on a bigger stage and with more people. the end game stuff is better and I feel better because I know I did this and that at a higher level in my opinion.