I have a bet with someone on the worlds hardest mountain to climb. I know this could be speculative, but what would generally be considered the most difficult mountain to climb? The most dangerous? I’m sticking with K2. The other party in a ‘size does matter darn it!’ attitude is sticking with Everest. Not that Everest is easy, but I was under the impression that it was about the 5th hardest in the world. Other than opinion, can anyone refer me to articles they’ve read on the subject or something somewhat concrete?
My brother, a fantastically accomplished climber, could resolve this definitively, were I able to reach him.
My understanding is that your question is too general to have a satisfactory answer. It depends largely upon which route one takes up a mountain, along with such factors as whether its done with bottled oxygen, with guides or porters, season, solo, etc…
FYI, the SE route up Everest is considered far easier than other Everest routes, but could hardly be considered easy, given the body count of big names.
My brother has climbed several man eaters. The ones I recall him being in most awe of include, IIRC, Shivling, Nanga Parbat, Trango Towers and Gasherbrum IV. In Europe, the Eiger north face, IIRC.
This article supports your position in the sense that it gives the reasons why Mt. Everest is not the most difficult from an experienced climber’s perspective.
Look down toward the bottom:
http://www.nepalnews.com.np/contents/englishweekly/spotlight/2004/jun/jun11/national4.htm
My favorite quote from that article
The mountain of love.
Well, stone mountain is made entirely out of granite, which is pretty hard.
Mount Viagra? 
Cerro Torre in Patagonia is a contender… only just over 10,000 feet but considered one of the most difficult peaks to reach on account of being ridiculously steep and pointy 
More pics here: http://wpni01.auroraquanta.com/pv/patagonia?img=1223
Those are some seriously pointy mountains…