Boy, engravers have it tough.....When you get to the top level, it's like saying one painter is "better" than another when you try to rank them. It is so style specific, it can easily end up a comparison of apples and oranges.
That being said, I tend to be VERY critical of the artistic composition of a piece. One thing I notice over and over, mainly on guns as there is more space to engrave, is wrong composition altogether. As an example. A pointing dog on point, with another dog behind him honoring the point, and a quail flying over both of them. It doesn't happen that way. My opinion is the engraver felt the need to do more than what was required to make the scene correct.
Anyway, I guess it really boils down to who is more collectible. Like Steven pointed out, if you had a collection with Churchill and Fracasi, you would be doing well. Add Torcoli, Ken Hunt, The Brown Bros. a piece or two from Creative Arts, a couple more from Sam Alfanao, Lindsay and Ron Smith, and maybe a nice .700 Nitro express Purdey Double rifle engraved by Phil Coggan and you would need to lend the collection to a museum occasionaly.
Of all of them, my favorite is Churchill. I've never seen another engraver who's artwork is as complete, elegant and correct. I've sat down with pencil and paper and tried to draw in his style while looking at a picture, and just couldn't get it there.