I'd have to say:
Obviously Geno Smith is at the top of the list. He's coming off a mixed season, where he was praised and doubted from week to week. He has to be more consistent this season especially with the upgrades on offense (Decker and CJ) I wouldn't be surprised if the Jets already have their eye on Winston, Mariota or Hundley three of the top possible QB prospects that will be eligible to declare for the 2015 draft.
Milliner is already starting the season off rocky. A high ankle sprain leaves him questionable for Week 1 and the Jets don't have much proven talent behind him. He was benched repeatedly last season and needs to prove he can be the No. 1 defender he was expected to be out of Alabama.
Decker was exceptional in the last two years. He survived the Tim Tebow era in Denver and was rewarded with Peyton Manning (talk about night and day). But how great of an impact is he going to have without Manning throwing pinpoint passes? Geno isn't the most accurate QB in the league. The new QB-WR tandem could struggle to build a rapport as strong as the Kerley-Smith connection.
CJ is coming to the Jets roster pissed. And rightfully so, he's rushed for over 1,000 yards every year with the Titans but Tennessee still didn't want to pay up. He's only 28 and still has a motor. Let's hope the Jets offensive line can block and create some lanes—if that's possible he'll record another 1,000 yard rushing season for Gang Green.
Antonio Allen is the wildcard here. The fact is he's a seventh-round pick that slipped through the cracks and has taken advantage of every opportunity on the way to the top of the depth chart at CB (Milliner’s injury still lingers) Shame on Kyle Wilson for allowing Allen to leap frog him from the safety position. Allen will make or break the Jets' pass defense. If he's talented enough at the position the Jets will be able to improve on that 22nd ranked pass defense last year.
I also put together an in-depth slideshow analysis on the topic: