I always start scouting in my office, in front of a topo map of the general area I want to climb in. I have found that the best, have a great full day of climbing trees, are in the bottom of valleys, particularly in finger valleys, box end. You can usually find at least seasonal running water in these areas, and my theory is that the larger number of trees is due to the forest traffic congestion. Where you have a valley the animals naturally move towards it in travel, at least in my experience, and therefore you have more seed, uh, deposits; which when added with water, you get trees!
I like to start my explorations in a couple of valleys, and also map a route to the nearby ridge line. I've found that I like camp sites on a ridge. The winds are better, the views are better, and there is typically less undergrowth, allowing for cook sites, and a place to pitch the tent, in case a sudden downpour soaks my hammock!
As far as the best tree, I'd say there are a lot of features to look for. First, architecture plays a huge part, Lots of limbs are great, but if they all run near vertical off the bole, then you are gonna not have a lot of options for movement, and most likely at some point you will be rescuing trapped gear. Second, views are important, this can be ridge lines, distant or nearby water, valleys, or even the possibility for wildlife encounters. Third a great tree takes some doing to get to. This for me is most important. I find that a 2 mile hike, a decent paddle, or just a short bushwacking expedition does wonders to take the edge off of my ever present wanderlust.
That at least is my "how to find a great tree" manifesto.
Climb Safe!
Icabod
Cam "Icabod" Taylor