I always model my characters T shaped hands down, this way the natural twist from your elbow to wrist is modelled with correct line flow, where as if you model palms facing the camera, the twist can usually be overlooked and cause problems when animating. I have found modelling in an A shape terribly awkward and pointless unless you do not plan on rigging the character and is basically a prop, as it can be a pain modelling the accurate deformation especially between chest and shoulder/arm pit area. It is by far easiest (for myself at least) to model arms spread T position hands down, that way the limbs are extended and you can further appreciate the muscular exaggeration rather than a relaxed pose.