I go for Daryl. Yes, the show is known for misdirect but I think they want the fans to outsmart themselves this time. ''Hey, it is Daryl and we make it dark to hide the face. The fans will then say, 'hey, the show is known for misdirect and so it has to be Dwight and not Daryl' .''

I do not think this is a valuable moment for Dwight to 'save' Rosita so as to reveal that he is now turning against Negan. I think that moment has to be more 'defining' and can be used in a more creative way. Throwing it out like this is a little waste, plotwise, I think.

Edit:-
Compare this pic at this link:-
http://www.walkingdeadforums.com/tv-series/is-this-daryl-or-dwight/
(turn up the brightness and contrast of your monitor if you can)

With this pic at this link (promo pic for 7-15):-
http://i.imgur.com/DrnWwiy.jpg
(http://www.walkingdeadforums.com/forum/threads/7-15-promo-pics.309092/)

And it seems the clothing is quite similar.

 

That was Dwight.

I'll go a step further with this theory: Rosita will be the one introducing TF to turn coat Dwight versus Ezekiel from the comics

 

I think it's Dwight, but I don't see Rosita getting captured at all. If she were, I think they would've ended the episode on that. He might be captured though.

 

Yeah, Rosita won't be captured. I agree with it being Dwight, and I think this opportunity will show us Dwight's first sign of betraying Negan and siding with Team Rick.

 

I agree, the only thing I'm unsure on is how Rosita will react, which is why I said "He might be captured." I can't imagine Rosita would be like "You wanna help? Well come on Dwizzle, let's go talk to Rick, and then I'll make you some celery soup casserole." She's obviously gonna be very wary.