The biggest problem I face with many character posing tools as that the shoulders and hips look horribly distorted when fully flexed. Look at the left shoulder, hip and knee in the picture below, to see what I mean.
I now believe I may have found a solution for this. To make the mesh deform most naturally, I believe the resting position should be halfway through the range of movement for every joint in each direction.
The problem is that most meshes are designed with the body in a 'neutral' T or A shaped pose - but that does not provide the full range of joint movement.
Think about the hip. Its greatest range of movement is forward flexion. From standing you can only bend your leg backwards about 30 deg, but you can bring your knee forwards, right up to your chest. To provide the full range of movement, why not design the mesh with the neutral position being half-way between these two extremes?
Ever wonder why the skin on your knees and elbows is so wrinkly? It's because you need lots of spare skin to allow the joints to flex fully, otherwise it would tear. The neutral position for elbows and knees is bent to about 90 degrees.
I would like to see a mesh designed to look good with the joints all positioned mid-way through their range of movement, with the hope that when the arms are fully raised or the hips are fully flexed, you don't get those horrible distortions. I have moved the right arm and leg in the picture above so that the joints are all mid-range.