While Applejack easily has the most brute strength, Rarity strikes me as the type of pony that would know kung-fu or something. Excluding unicorn magic, this is a case of strength versus skill. My money is on Rarity.
Rarity: "Yippee ki-yay, my dead, illiterate Applejack!" "Howdy, pardner!" "Happy trails, laborer!" "Did I throw a 'wrench' into your plans? (laughs maniacally)" "Not much of a quick-draw, are you, pardner?" "Giddyup now -- to hell!"
Applejack: Now just stop trying to mess with my contraptions. It ain't gettin' any harder for me to kill ya! You know where you oughta hide next time? Back in France. Dominated, you turncoat! Dominated, you snake! This skunk's startin' to smell. Slither on back to hell, Rarity! That's what my daddy taught me to do to backstabbers. You're a looong way from France, girl. Don't go meddelin' in my business. You are a coward an' a scoundrel. If y'all had more gadgets for killin', you wouldn't need so many for hidin'. I just beat on your sneaky ass like a mule, girl!