My vote goes to the Saddlebred. I own 4... Because, of the many breeds I have worked with, the Saddlebred has utterly charmed me. I do not, nor have I ever ridden Saddleseat. They are not a truly gaited breed, very few individuals gait "naturally".
Sport bred individuals of the breed are heavier in bone than a TB, but have a TB type body and often excel at jumping. (Looking at their conformation it's not really hard to see why either) they were once bred as military mounts - because their easy gaits were comfortable to ride all day, they had power, speed, courage and a will to please. Not that many years ago the breed was a favorite for puissance jumping (the one where they jump impossibly high walls) , many horses of that discipline were full Saddlebred or part breds.
They do well in endurance (I know my own sure can go and go and go...)... I do dressage, game, jump, cross country, western pleasure (open classes, not breed classes), I have used them to round up sheep. They have started getting major recognition in the combined driving sport as well.
None of mine are what I would call high strung, or skittish, and ALL of them are very intelligent. So far I haven't found anything they won't give a try to... And with all their being. They make a fine competition mount, then are able to go home and give pony rides to the whole family.
(Ok, sales pitch over .... )