I think Lily Allen is a better writer than all 3 combined. You're always gonna find a better writer or a better singer and a better performer if you look for it.

As far as the 3 you mentioned, Kacey Musgraves is more my style. I love her. She also co wrote Miranda Lambert smash hit Mamas Broken Heart. That is an awesome song. BUT. Taylor is the youngest to write a number 1 hit by herself and perform it (Our Song). So you can't look past that accomplishment. Carrie? Not even close to those two in songwriting talent but she seems to be progressing.