Was going to suggest this along with some pulleys and straps so you can somewhat affect the route (of course you'd have to stop and go change the setup before sled hits the pulley).
If going with capstan I'd try to (temporarily) attach it to the sled and use it "backwards". So you'd be at the sled all the time and able to spot any problems (get the excess rope in sled). With capstan and plenty of trees around I'd only get 100m of rope and make multiple pulls if longer distance.
Having choice of truck, quad and capstan it's that order. And even initially using capstan we've always used the truck once close enough. And that's with several people so there's always few at the sled/carcass (communication with radios).