I find comfort, particularly when you like long rides, is paramount. One can always shift one's position around dynamically to compensate when situations dictate. I prefer my h-bar height to be at, or slightly higher (maybe less than an inch) from the saddle's level position. Any higher and I find too much pressure on my sit bones. Any lower and I find more pressure on lower back and neck. It's true that when climbing, the front end can wander if your bars are too high. This is assuming you stay static on the saddle. However, when climbing steeper sections where front end wandering is likely, I scoot my butt to the nose of my saddle. This keeps power /traction on the rear wheel, while weighting the front wheel to prevent wandering. Works perfectly, plus works a different set of leg muscles.
One other note....whatever position you decide is best, keep in mind that for a hardtail you want to compensate for sag. So, if you decide you like your h-bars level with the saddle, and your fork has 1" sag when you're on the bike, then you might want to set your bars about 1" higher so that, when sagged, the bars are where you want them. For rigid (no sag) and full-sus (dual (and more or less equivalent) sag), you could leave them level to saddle. DH bikes are a different story, I have no experience with them animals. Good luck.
