I like to be 15' up in a tree larger around than my body profile.  Then I feel like the tree blocks some of my outline, especially from behind.

I like TJ's plan, for me a hemlock or cedar. For me it is not so much about height as it is about cover. I may have to go 25 ft. to make sure I have cover or am broken up by the tree, I may have to only go a few ft. and that is enough. That said I do hate the steep angle created by being high, but I deal with it if I have too and will let the deer get out aways before I shoot rather than that real steep angle.  Shawn

I usually go higher..about 18-20 feet, but prefer(in a perfect set up) to be 15 or so high and 15 yards away if possible to a hot run or area. I like a spot with strong thermals, so even if the winds are swirling my stink will be carried UP before they get it at this distance.
I love cover, to hide my stand from potential thieves and not catch the eye of the very wary bucks around here.  Small hang on stands with screw in steps, wedged into the thickest hemlock or white pine I can find. If none, I try to get into a cluster of two or more trees, the extra trunks really help break up outline and movement.

Good thermals are my biggest advantage, deer around here meander more than following a set path. They come in from any direction.

90% of the time, in a Loc-on, 100 yards from thick bedding area leading towards the most active feed tree (wind approving of course).  10% of the time, anywhere there is a doe in heat!

90% of the time I use a climber. 15'-20' up and about 15 yards from trail. I really like a small beech next to my climbing tree for cover but over the years I worry less about cover and more about places with consisant wind.


Rob

all great info- from hard earned experience.
generally i get the feeling people would rather be a bit further out, and slightly lower- to make the better double lung shot- and obviously cover is of utmost importance!!

I like a multi trucked tree.  12 to 15 feet and around 15 yards from the trail.   with lots of back cover.

I like all the ideas above, except that many times they are not available options. So I just do the best I can. I will hang a loc On on a tree without much cover if I have backgound so I am not skylined. I prefer about 15-18 feet high about 15 yards from where I expect a shot.
Right now I have a stand in an 8" cottonwood tree, 9' high. I am surrounded on the back by cedars. If I go any higher I will be skylined and out in the open. Because of the area a deer cannot come thru more than 15 yards away.

For the stand itself, I'm a big fan of Lone Wolf Alpha stand.  It's big enough for my size 13 boots and they're quiet, period.

For the tree, I prefer pines, hemlocks or cedar OR a regular hardwood tree next to a couple of the above that will give me a good backdrop.  Height depends on the trail location and cover.  I probably average 12-15 feet to the base of the platform.  I've got a couple at 20 feet.  As noted above watch the shot angle.  The higher I am, the farther from the trail I like to be. 15-18 yards is probably my average.  

Don't underestimate the use of a ground blind on a embankment/hillside above a good trail. I've got a couple of spots that are about 20 yards off good trails that are 15-20 feet down a hillside with some juniper/small cedars around the back of the back/sides of the blind for cover. I just dig a comfortable seat into the side of the hill and put a little cover out in front for an effective blind and avoid being in a tree that does not provide good cover.  This is especially important in the late season when there is no leaf cover.  I think at that time of the year, a good ground blind is much better than a marginal tree stand setup.  

Also, for those 'permanent' funnel locations that have good trees I like to set up a ladder stand to get to height I want and then put a Lone Wolf stand off to the side that I can step onto. I like the ease of climbing up and down a ladder stand, but don't like sitting on them or bow limb clearance on some.  Usually you can find them for 60-80 bucks on clearance at the end of the hunting season at the various box stores.