As a guy who’s played the guitar for probably a couple thousand hours over 30 years, I hope you won’t mind if I add another perspective or two to this conversation.
First, the requested favorites, in order:
Hendrix- what sets him apart from the others is his ear. He seems to have some god-given skills that the others lack - a soufullness, melodic inventiveness and improvisational ability that maybe has yet to be equalled. Never mind all the noise and feedback, or that Everybody and His Brother can now do a passable imitation, just listen to “Red House” on “Isle of Wight” for an idea of what one man can do with a guitar:
http://www.youtube.com/watch?v=3IDd6QPFAz0
Duane Allman- could be pretty pedestrian at times, and would be nearer the other end of my list, except for his divinely inspired playing with the slide. Listen to “Statesboro Blues” live for a sample (couldn’t find a link).
Eric Clapton- until Hendrix came around, it’s said that you’d see the infamous “Clapton is God” graffiti all around London city, and not for no reason. His early stuff with the Bluesbreakers and Cream was pretty damn intense. This version of “Crossroads” isn’t the iconic one, but it’s still pretty cool: http://www.youtube.com/watch?v=Cm3Er3F51cA
SRV- mostly a master regurgitator of other people’s styles, and could channel Hendrix or Albert King endlessly. Can summon a lot of intensity, but I’d call him the least unique voice among the bunch.
Page- as a soloist, doesn’t bring enough fire to really catch my ear (except in a few instances) but shines as an all-around musician. When you factor in his abilities as a composer/arranger/producer, you’ve got a true renaissance man, one of the most talented and influential rock icons ever.
Now as for the question of skill, none of these guys presents any real problems for me in terms of how hard their stuff is to play*, with the exception of Stevie Ray. His hardest stuff is very precise and takes a bit more work - even on light gauge strings, and SRV played with impossibly heavy ones - which distances him from the pack, followed by Hendrix, and then the rest. The gaps aren’t huge, though - they’re all good.
*Shawn Lane or Danny Gatton, OTOH, I guess I’ll never catch up to.