By Mel Kiper Jr. Special to ESPN Insider Practice week at the Senior Bowl is all about identifying the top two or three players. It's a great setting to determine how prospects respond to competition and who can thrive in an NFL-type environment. Two players have definitely answered that challenge. Mark Clayton Mark Clayton is getting a grip on Senior Bowl week. Oklahoma wide receiver Mark Clayton has been the best offensive player on the field. He has great feet, runs good routes and has phenomenal hands. He completely schooled Howard DB Ronald Bartell Jr. Clayton is not real tall or fast, but he is quick and ready to play. He is solidifying himself as a late first-round pick. Iowa lineman Matt Roth has been the best defensive player on the field. He is a relentless, determined pass rusher. Roth is quick off the ball. He basically beats the offensive tackle out of his stance. Ross is fiery and intense. I think he is the best defensive player at the Senior Bowl and a solid first rounder. North practice notes Vincent Jackson from Nothern Colorado has great size (6-5, 225), but he doesn't look real explosive out of his break. He has not looked super quick and has not separated well. You have to expect some nerves because he is a Division I-AA kid trying to prove that he belongs. It will be interested to track his progress this week. WR Brandon Jones from Oklahoma made some real nice catches on Tuesday and looks like he is making a move up the board. Courtney Roby, a wideout from Indiana, looks like he is pressing a bit. He has had a few drops. Roby needs to relax and pick up the pace. Purdue wide receiver Taylor Stubblefield is quick, has great hands and runs good routes. He is very polished. Stubblefield caught a ton of passes in college from Kyle Orton and is showing in Mobile that he can get open against the best players in the nation. I think he will be a very interesting selection in the fourth or fifth round. TE Alex Smith from Stanford has not shown big-time quickness and is having trouble separating. He does catch the ball pretty well, but Smith needs to get after it a little more. Michigan center David Baas is not real athletic, so he will struggle at times in one-on-one drills. However, he is a super tough player and will play better when he is around an offensive line that he knows. Baas will be a good second-round selection for some team. Cal DT Lorenzo Alexander is not real strong, but he gets good initial leverage and has good technique. Howard CB Ronald Bartell Jr. has some physical ability, but is very raw. Antaaj Hawthorne is a quick, strong kid from Wisconsin. The defensive lineman worked against the double team a lot in college and knows what he is doing. Hawthorne works hard and has good technique. With a strong combine, he could easily end up being drafted in the middle of the first round. Akron quarterback Charlie Frye has been OK. He hasn't been spectacular, but he hasn't been disappointing either. I'm interested to see how his week progresses. It's important to remember that the quarterbacks are trying to learn a whole new offense while working with new receivers and running backs. They have to get their timing down. It looks like the QBs at the Senior Bowl are thinking too much right now. They are not just reacting. UConn signal caller Dan Orlovsky has been hot and cold. He needs to add some pace to his setup in the pocket. Orlovsky needs to add some more consistency to his game down here. I like Purdue quarterback Kyle Orton, but I don't think he will go as high as former Boilermaker QB Drew Brees, who went with the first pick in the second round. Orton will probably go later in the second round. He has an elongated delivery and doesn't snap it off from the ear. However, Orton is accurate, makes nice decisions and quick reads. South practice notes Auburn quarterback Jason Campbell is here trying to build on his dramatic rise up the draft board during his senior season. Some could argue that he is a one-hit wonder, but Campbell threw the ball pretty well in practice on Tuesday. He's big and has a nice arm, but is a little mechanical. While he is inconsistent at times and is still a work in progress, Campbell could be a solid second-round draft choice. David Greene is not mobile and doesn't have a big-time arm, but the Georgia QB has good size, sets up well and has good accuracy. Mechanically, he is very sound. Greene is advanced from the knowledge standpoint and makes quick decisions. He is intriguing. While doesn't have the wow-type physical attributes, he was a big-time winner at home and on the road in college. He looks comfortable under center and is playing like he belongs here. I think he has elevated himself to the third or fourth round. Georgia WR Reggie Brown is a big kid with good speed. He separates well from the cornerback. I questioned his quickness out of his cuts during the season, but he has shown that he has that ability down here. He is running precise routes. Brown has good hands and is a great blocker. There's a chance that he can move up into late first or early second round. He has really helped himself and can help himself more at the combine. WR Fred Gibson, Brown's teammate at Georgia, is tall and angular with spindly legs. He has good speed and very good athleticism. Gibson has showed a good burst after the catch. He's an interesting prospect. Look for him to go in the third round. Texas A&M WR Terrance Murphy suffered a groin pull and will not play any more this week. Tulane wideout Roydell Williams has replaced him on the roster. Florida State WR Craphonso Thorpe has had a so-so week so far. Roddy White, a wideout from UAB, was off to a great start to the week. White looked like one of the best players down here, until he tweaked a hamstring. I still feel like he can be a mid-first round pick. USC tight end Alex Holmes looks a little heavy. He lumbered a bit getting into his routes. Holmes has shown good hands, but he's only an average blocker. With a nice week, center Jason Brown, from North Carolina, has a chance to end up in the second round. He had a nice career with the Tar Heels and has good skills. He needs to finish strong. Florida State's Bryant McFadden is one of the most aggressive corners at the Senior Bowl. He has shown that he can really deliver a hit. In fact, McFadden has been looking to make a big hit on every play. He has a chance to be a late first- or early second-round pick. LSU corner Corey Webster has a high grade coming into the year, but he was slowed by minor injuries and did not play to the expected level. Webster has been OK at the Senior Bowl, but has not really stood out. He might have lost some confidence because of the injuries. Webster needs a strong finish to guarantee a spot in the second round.