I think in EVERY way that AppleJack would win. AppleJack uses manual labor ALL day pretty much. While RainbowDash sleeps in the clouds -_- Now, RainbowDash and other Pegasus are hollow boned, so they can fly easier and faster. With one kick from AppleJack all RainbowDash's bones that made contact with AJ's leg would break easily. And also... Have you seen how easily Pegasus wings break?? In countless episodes of MLP I have seen a Pegasus wing break. Due to the hollow bones. And if AppleJack did ground her with her lasso (that she is very good with) it would probably snap RD's wings just from the pull down, and if it didn't break her bones, the lasso that AJ has everywhere she goes would be around RD's wings making it a guaranteed victory for AppleJack, the strong manual labor workhorse.
PLUS AppleJack is WAy smarter then RD! RD would lose control very very easily.