Typically a question like this is kind of a formality as it is typically the teams' first round pick, and if it's not him or like the Redskins the team doesn't have a first round pick then it is the 2nd rounder. I don't think the answer is that simple for the Redskins this year. Not only do the lack the first rounder, but they took high risk/high reward picks. So everyone could make a case for having a stellar season or a disappointing one.
2nd Round CB David Amerson:
Why it could be him: Amerson was a ball hawk at the college level, leading the NCAA in interceptions his sophomore year. He's the type of guy who is capable of coming up with multiple big game defining plays over the course of the season. Amerson is also a corner who is adept at getting big returns after interceptions and could add a defensive touchdown or two, to his stat line.
Why it won't be him: Amerson is a feast of famine type of cornerback, and too often this past year it was famine. As much as he's capable of making game defining plays, he's just as likely to give up game defining plays. It's an inconsistency in this game that could lead the team to decide that he's best served as a reserve behind DeAngelo Hall, Josh Wilson and E.J. Biggers this season while he develops. He very well might not even see the field enough to warrant consideration of the best rookie season.
3rd Round TE Jordan Reed:
Why it could be him: Reed has a lot of potential in that joker tight end role and could be a weapon that creates major match-up problems for opposing defenses. He could quickly become the Redskins number two target behind Pierre Garcon, especially if Fred Davis doesn't recover well from the injury. Reed could also be a big Red Zone weapon, not just with his receiving skills, but some trick plays involving his rushing could be in the works as well.
Why it won't be him: Reed has a lot of promise, but he's pretty raw overall, given that he started his career at Florida as a quarterback and dealt with some injury issues slowing his development in college. If Fred Davis is healthy it will make it hard for Reed to make an impact. Also, the Redskins have never really been a team to involve two tight ends in the passing game at the same time, so if Davis is the number one, there will be few targets for the rest of the TE's. Finally, the Redskins are a run first team, and Reed's lack of blocking ability could make him a liability if he's out there too often.
4th Round S Phillip Thomas:
Why it could be him: Thomas has a really good chance to start next season, something that isn't as clear with the two rookies ahead of him, or any of the players picked behind him. Thomas is a ballhawking safety so he definitely could come up with his fair share of turnovers next year. Thomas has also shown himself to be a quality blitzer so he could add some sacks next season as well.
Why it won't be him: Though he has the potential to do it, Thomas is probably miscast if he's forced to play free safety next year. While he may still be the Redskins best option in that role, he will probably more likely suffer growing pains in that position.
5th Round RB Chris Thompson:
Why it could be him: Thompson has game breaking speed and could have a major situational role on the offense, both as a runner and receiver. Though his touches won't be starting level, he could come up with some big gains and huge game deciding plays. Thompson also could potentially be used as a weapon in the return game as well.
Why it won't be him: Thompson is coming off back-to-back injury shortened years, including an ACL injury this past year. Though some can return at 100% after an ACL, 9-10 months after the injury, the majority of guys still struggle that first year back. Especially in the case of a guy like Thompson who's entire game revolves around speed and lateral quickness. At the very least Thompson will be behind due to missing all the offseason work leading up to training camp (and he might miss some time there as well). It's also unlikely that he'll be able to take over return duties since he doesn't have collegiate experience and likely won't have the time to work on it this offseason.
5th Round OLB Brandon Jenkins:
Why it could be him: Jenkins would have been a lock for the top 50 picks and likely a first round pick, had he not gotten injured the first week of the season this past year. He had a dominant sophomore campaign and a really strong junior year, prior to the injury. If he's fine, he could be a valuable situational pass rusher for the Redskins, particularly early on when Rob Jackson is suspended. Even though he's not going to be a starter, Jenkins could contribute 5+ sacks if given the opportunity.
Why it won't be him: Though other teams might do it, the Redskins haven't really shown many looks of bringing in a third edge rusher on passing downs. While Jenkins could fill in for Brian Orakpo and Ryan Kerrigan some, barring an injury it is likely to just be a handful of snaps, especially once Rob Jackson comes back.
6th Round S Bacarri Rambo:
Why it could be him: Rambo is possibly the best natural free safety on the team and has a big history of making big plays. If Thomas can't handle the free safety role, Rambo could get a shot at it. If so he's more than capable of showing his range and coming up with some big turnovers. Rambo also is a guy who is known to defense routes as well, and not just always go for the pick.
Why it won't be him: Rambo has had off the field maturity issues which caused him to slide in the draft, if there are any further issues it could lead him to being benched or suspended. Rambo also has two areas of concern in his game as well. For one thing he tries too hard to strip the ball, which could lead to some missed tackles and extra yards for the offense. Also, Rambo struggled at the Senior Bowl, particularly when asked to man up with tight ends and receivers. Finally, it is very likely that Rambo just won't have the opportunity to play enough as a rookie.
7th Round RB Jawan Jamison:
Why it could be him: Jamison comes from a zone blocking scheme and is a perfect fit for Mike Shanahan's offensive system. Knowing the track record Shanahan has with late round running backs (and just rookies in general), you have to feel good about Jamison's chances. Though he should just max out as Alfred Morris's back-up, the reality is at RB the back-up can quickly become the starter. While Morris was 100% healthy last year, he might not be as lucky this year. In which case Jamison could fill in and put up some really good numbers.
Why it won't be him: Though Jamison is a really good fit for Mike Shanahan he will still start out on the depth chart behind Morris, Roy Helu Jr. and likely Evan Royster. Unless he has to, Mike Shanahan typically has not relied upon rookies (other than first rounders) with the Redskins early in the season, so Jamison's attempts could be way down, even if Morris were to miss some time. If Morris is healthy and Thompson is the change of pace/specialty back, it will likely limit any chance of Jamison getting the opportunity to be the best rookie.