In the Belichick era, here's my list:
BEST
1. Brady. 199th pick in 2000, 140 career AV, 2 all pro teams, 8 pro bowl teams, 2 MVPs, 3 Super Bowl titles. Best pick (especially considering where he was taken) in the history of the National Football League.
2. Seymour. 6th pick in 2001, 90 career AV, 3 all pro teams, 7 pro bowl teams, 3 Super Bowl titles.
3. Vince Wilfork. 21st pick in 2004, 74 career AV, 1 all pro team, 5 pro bowl teams, 1 Super Bowl title, and still has (barring injury) many more productive years to go.
Honorable Mention: Rob Gronkowski (42nd pick in 2010), Aaron Hernandez (113th pick in 2010), Nate Solder (17th pick in 2011), Sebastian Vollmer (58th pick in 2009), Jerod Mayo (10th pick in 2008), Deion Branch (65th pick in 2002), Matt Light (48th pick in 2001), Logan Mankins (32nd pick in 2005).
Worst
1. Terrence Wheatley, 62nd pick in 2008, only played 12 games in the league.
2. Chad Jackson, 36th pick in 2006, only played 18 games in the league.
3. Marquise Hill, 63rd pick in 2004, only played 13 games. I know his situation is different in that he passed away suddenly and tragically, but if we are evaluating picks, this turned out pretty badly. Kind of like the Len Bias pick (though Bias was far more of a sure thing than Hill)....seemed like a great pick at the time, but for obvious reasons it ended up being bad. I really don't mean this in bad taste.