The saddle that will work best for long distances is the one that fits you best.
Don't be shy about posting your sit bone measurements. Heck, I've got the widest span of all, and I'm not shy.
SEVEN AND A QUARTER INCHES, EVERYONE!!! LOOK HERE, MINE ARE 185 MM OUTSIDE-TO-OUTSIDE!
As you can imagine, having sit bones wider than most saddles did cause me some difficulty.
Brooks B67 and B68 really and truly fit me. If your span is anything like mine, that's where I'd suggest you start. If you need a cut out, the B68 is available with cut out. Sprung or unsprung is a matter of personal preference. I like sprung best, but that's just me. I don't like short noses (short so skirts don't catch) so I stayed away from the B67-S and B68-S.
For rides of more than 50 miles, my favorite saddle by far is my Brooks B67.
www.wallbike.com:
www.wallbike.com gives 6 months free trial on saddles.