McD's passing attack schemes frequently use ALL potential targets pretty much everywhere in formation, including TEs and RBs (even Dwayne Allen and Develin have been split out to the X). So, I tend to avoid being quick to pigeonhole guys as to where they'll line up.
That said, each of these guys may be most optimally used out of certain spots. So, going at it from that direction:
Hogan = X or Z equally, but probably some Y, too
Britt = Z, X, maybe some Y occasionally
Patterson = Z or Y
Decker = Z or Y
Edelman = X, Y or Z
Dorsett = X, Y or Z
Projecting Berrios/McCarron as Y or Z (McCarron got smothered at the LoS by Lewis in press on one play in practice).
To me, one of the primary requirements for the guy lined up directly on the LoS at X is the ability to consistently break close-proximity press-man coverage. The guy can either juke his way past it (Kenbrell Thompkins had one of the sweetest moves I've ever seen against the press out of the X), or muscle his way past it. However, a guy who muscles his way past press can still have his route-timing disrupted, simply from being physically engaged momentarily (although Brady seems to possess an uncanny ability to notice this pre-snap and to adjust his read-progression and timing to compensate).
OTOH, the Z (flanker) spot offers the receiver at least a one-yard cushion for his first step, so guys who may not be consistently successful against press can still run pretty much the same routes as the X. The Z spot also offers more opportunity for the receiver to take a "fake" step downfield, and then catch an uncontested quick forward pass behind the LoS and run with the ball. I suspect that Patterson may be the receiver on several such plays over the course of the season.
I'm not super familiar with what the Pats use for their terminology, but the Y is normally the TE. The slot, which I think you're alluding to, is the U. The U could be the 2nd TE or the slot WR, depending. That's using terminology that is frankly outdated though.
There's something to be said for your take on how the Pats move guys around formations, and I definitely wasn't suggesting that they could only play that one position. I was more trying to identify guys by the types of uses you'd have for them.
The X is the guy who's on the weakside of the field, who's against the line and needs to be strong against press, like you said. In this offense, it's a bonus if he can stretch the field. In many traditional offenses, he's your best WR. Think Calvin Johnson or Plaxico Burress. The idea of a 'true #1'. (I personally think 'true #1' WRs are a huge waste of money compared to what the Pats can scheme up)
The Z is a motion guy (in a 2 WR set). He's running shorter routes, is potentially a little weaker, and he's a playmaker you want to run with the ball after the catch.
With these roles in mind, a 2-and-2 3WR set is largely like having 2 X's on the outside and a Z in the slot. If the 3WR is your default set, it's a little disingenuous to lay out the starters the way that I did.
More of a pure slot guy is just like a Z, except he's definitely not someone you want playing X. There are guys who can play X or Z (most WRs, historically), but then there are some that you reaaaally don't want to put in the X position. Then, you keep them in the slot the entire time, and they never find themselves running routes on the empty side of the field or doing the tough things an X might find themselves in.
It's tough to say which three I'd pick at WR, even if we're just talking before Edelman comes back. I think Patterson is a better scheme fit, but Britt has the more proven track record. Then you have Hogan, who doesn't have a lot of amazing games on his resume, but he's extremely solid, reliable, and he knows the system very well. Then there's Dorsett, who's still young and coming into his own, and he might in fact be a rather good scheme fit. I'm still not sure how to categorize Decker because I don't know what the state of his body is.
