APS-C format has nothing on full-frame no matter which way you go.
Actually, smaller sensors have many advantages over the full frame. In sports photography, the advantages come with the wider DoF and the advantage with faster framerate which is very important.
AFAIK, most professional sport photographers like to use a smaller sensor than Full frame. I would guess APS-H to be the most popular choice. However, the selection of wide angle lenses is poor for this sensor size. Therefore I personally prefer the APS-C for skydiving. The weight issue doesnt really matter that much for me, but its a plus.
Also, using manual focus will most of the time be focused "around there", but isnt really spot on. Makes it kindof useless to spend a lot of money on an expensive body, if you are not able to focus 100% I have seen many skydive photographers spending a lot of money on an expensive body and L-series lens and then shoot off focused photos on manual.
(This post was edited by BMFin on Feb 28, 2013, 4:59 PM)