One of the guys who works on the show does humanisations, so I'd consider them the closest we have to canon. His Pinkie basically looks like a gymnast which makes sense to me.
In terms of physical strength, Twilight is known to be considered a weakling and Rarity also struggled with Tom, indicating that they are tied for last. Rarity is better at physical combat though.
AJ is the strongest, but RD comes close. Pinkie should have earth pony strength, supported by her acrobatics, but she may have nelected some physical strength training to develop other earth pony magic.
In combat power, Twilight has just reaserted herself as number one with the stuff she pulled this episode including launching the library into the air. Add what she did in Boast Busters and remember that that was before her massve increases in power as well as what she pulled off as a filly and the fact that she
can catch RD and erect omnidirectional forcefields which protect a head able to take anvils, pianoes, wagons, etc. and she's very hard to beat.
Pinkie is almost as fast as RD, has teleportation, multilocality, hammerspace, a weapon, can fly through machinery and almost through bouncing, perfect disguises, elasticity, precognition and apparent super strength. She comes next.
RD has hypersonic flight, can destroy barns, fly into the ground at hypersonic speed without being injured, is agile, has superstrength, can vaporise barns, split rock and shake mountains from a distance. She also has a black belt in Karatee. She's next.
Applejack has speed rivalling RD's, is the strongest of them all and is clearly very tough as well. She also knows boxing. She's next.
Fluttershy has flight, the ability to communicate with animals, has super strength and The Stare. She's next.
Rarity has fine-manipulation telekinesis, was still able to carry Tom and knows martial arts. She's last only due to how insanely powerful they alll are. And if Rarity has the option to use social-Fu... well, she'll easily take care of business most of the time.