It will be interesting to see this battle unfold. Woods is an almost lock for the 'Z' receiver. He's been consistently talked about as the most NFL ready rookie wide receiver this season. The 'X' receiver position is up in the air. In order to understand the competition, we have to understand the position. This player is going to be on a lot of backside throws (Posts, digs, verticals, etc.) They also need to be a solid blocker.
OTA highlights showed Graham playing well.
Goodwin was highlighted for being an outstanding blocker.
Da'Rick Rogers is someone you haven't mentioned, and also my favorite to win this battle.
http://queencitysports.net/the-x-factor-which-buffalo-bill-will-play-x-receiver-in-2013/
This link breaks down each receiver and their measurable, skills, production in terms of necessity for an 'X'