I ride in a Hillason treeless saddle, which is VERY comfortable, not the choice for all horses though. Treeless saddles can be bad for certain horse shapes because of weight distribution....so I'd keep an eye on the sweat patterns and such, especially if you're doing endurance or CTRs. Judging by your picture rider weight wouldn't be an issue, but I've also heard from some people that nobody over 170 should use a treeless??? Not sure how much truth there is to that. Probably again depends on your horse's shape and how the weight would be distributed.
Basically, any endurance saddle, treeless or not, english or western, will be more comfortable than a normal saddle because they're meant for sitting in for hours and hours on end. =)