I go with my eye test
Wright was the best starting pitcher until 5 starts ago, when he started pitching poorly (I realize he may just had one blow up inning). Porcello to me always throws strikes and I like that about him. Price pitched badly at beginning but got the run support, pitched better afterwards but did not get the run support and now is on a downward trend again.
If Pomeranz has a good outing and returns to his norm for the season, then Price is dead last, 5th starter. Ever since E Rod has given up throwing change up and focused more on slider, he's pitched better.