For as simplistic a measure as it is (and not a true measure I know - there's more to a wingers job than scoring tries) let's just take a look at the try scoring stats of the 3 wingers in question in competitive games (there's a fairly even standard in the competitive games, the friendlies not so much). In that I'm including 6 Nations, RWCs and AIs.
Trimble:
Starts - 15
Subs - 5
Tries - 2
Fitzy:
Starts - 12
Subs - 2
Tries - 2
Earls:
Starts - 9
Subs - 4
Tries - 3
In this department the tiering would have to be Earls, Fitzy, Trimble. The only things I think Trimble offers that the other 2 don't are physicality and aerial ability - Trimble seemed a good restart option recently. My preference coincidentally matches the above though. I think Fitzy is the best defensive option and Earls the best attacking option. That leaves Trimble sort of hanging around the back somewhere I'm afraid.