For me, I've always just been a raider. It has been a huge part of my enjoyment with the game, second only to the story and lore of Warcraft. I've also always been a large group raider from Classic World of Warcraft right up to Mists, but I did always run with a 10-man group right up until the point where 10 and 25 started to share a lockout, just so I could keep raiding and so I knew how to handle both situations. Recently, due to personal scheduling reasons, I've had to make some changes to my World of Warcraft playtime that has resulted in not only me re-joining the Horde, but also having shifted from 25-man raiding to full time 10-man healing on Lodur.
This post is just my opinions and observations based on my own change from 25-man raiding to 10-man raiding. Your mileage may vary.