My nephew has a Haflinger we often use on some pretty tough trails in the AZ mountains. He seems to handle things well. He stands about 15+ hands and weighs-in at about 11-1200 lbs, but his barrel is not much bigger than most QHs. He just has massive chest and rump muscles, stout legs, and large hooves. He is a very inquisitive horse and tends to break things, sort of like a 2 year-old kid. He'll put his hoof on a box or something and see how much weight it will take to crush it. If that is your lunch box, or tool box...well, you see what I mean. He will lean on fences until they break. Not a mean bone in his body, just curious...and very strong.
My dad has an old boat trailer in the corral where he is kept. We often look outside and see him standing in the middle of it. He just steps in, tries to break something, then walks out the other side. That's exactly how he is on the trail. He prefers to push stuff out of the way rather than walking around. Nothing riles him.
He is not a fast walker, although he has the ability to go at a pretty good walk...if he wants to. He would rather walk slow, then trot to catch up, and I defy anybody to be able to convince him to do differently. He will walk along beside, behind, or in front at anytime. He will keep pace with a normal QH, but gets behind with one with a good stride.
Overall, thumbs-up on him as a trail horse, but you have to pay attention to him. He breaks stuff. You either keep him tied at night, or inside an electric fence. Oh, and as a pack horse, he's great. He can carry twice what most horses can carry, and do it all day long.
We feed him the same as our other horses when we're out on the trail and he seems to keep his weight, but I've never had him out for more than a week.
The mule in the pics is about 13.5 hands or so, for comparison. My buddy in the green-striped shirt is about 6'4" and 230 or so.