Hello all. First off, let me tell you about what I do. By day I am a financial and business analyst. Basically I analyze data to help improve a fortune 500 company, so to say I am well ad versed with data and reveling the story I tell would be an understatement.
This forum, and a lot of the world of Warcraft community, seems to always get into a big uproar over the 10 vs 25 man debate, for reasons that are quiet obvious. People want to think what they're doing is "harder" so it makes their kills more legitimate and them more special. So what I decided to do, was bring this wonderful tool, wowtrack.org, which if you haven't seen, already breaks down the difficulty index of each boss based on kill numbers. The kill numbers ARE valid data, because it seems for just as many casual guild 10 mans there are, there's 1 25 man that equals out in equilibrium. Which, the ratio btw is 14.66~/1 guilds, with the numerator obviously being number of 10 man guilds compared to 25.
Anyways, without further ado, here is the rankings -
http://www.wowtrack.org/encounter.lua
More Difficult on 25
Heroic Morchok
Heroic Yors'ahj
Heroic Warlord
Heroic Ultraxion
More Difficult on 10
Heroic Hagara
Heroic Warmaster
Heroic Spine of Deathwing
Heroic Madness of deathwing
http://www.wowtrack.org/encounter.lua
Data's all there. It's a clean split, with the 10 mans getting the harder content later in the Dragonsoul.
Please do not start a 10vs25 war. This is data driven only, if you have other analysis to add, i'd love to hear it but please don't spout out baseless opinions. Just because you did one difficulty the first time then switched to the second is NOT indicative of how difficulty the fight is due to the human learning curve for each boss. Thanks!