Per Fox Sports and Bill Barnwell (of Football Outsiders fame):
Best overall pick: DB Darrell Green, Round 1, Pick 28, 1983
Will be a first-ballot Hall of Famer in 2008; again, much like Slater, guys who spend forever playing for the team that drafted them are infinitely valuable and special for a variety of reasons.
Best value pick: QB Mark Rypien, Round 6, Pick 146, 1986
While Mark Schlereth was a little more valuable than Rypien, 45 percent of his career was with Denver, 45 percent was with Washington, and 10 percent will be as a cadaver.
Worst pick: T Andre Johnson, Round 1, Pick 30, 1997
Johnson never played for the Redskins, instead appearing in four games as a Lions player before vanishing. Here's a line of busted first-rounders: Desmond Howard (No. 4 overall), Tom Carter (No. 17), Heath Shuler (No. 3), Michael Westbrook (No. 4), and Johnson.
Post merger the only person I can think of who could compete with Green is Art Monk, who at least deserves mention for helping us reach four Super Bowls, winning three. Still, Darrell Green likely gets the nod. He did play in three of our Super Bowls and was more productive in those games than Art Monk was in his. He is considered among the best DBs of all time. The most compelling argument for him, provided by Barnwell, is his longevity with this team. Perhaps never in the history of the NFL has one player provided so much for one team, given that Green stayed with the Redskins through 20 seasons, playing in 295 games. 15 of those 20 seasons he played all 16 games, and recorded interceptions in 19 of them.
If we're going pre merger, than I think Sammy Baugh deserves consideration. I still consider him the best QB ever given how he defined the position and for how long his records survived the test of time, even as the game evolved and changed drastically in favor of those who inherited it after him. Slingin' Sammy remains the only Official Retired Redskins Jersey although there are many unofficial retired ones, including Green and Monk. Baugh spent his entire playing career with the Redskins over an impressive 16 year career. Does that push him over Darrell Green? Reader(s) decide, but he deserves consideration at least.
I dig the Rypien pick as best value, as a 6th round Super Bowl MVP is always nice to have (only Tom Brady and Kurt Warner come to mind?). The only other person I think is in the conversation is Dexter Manley, a 5th round pick in 1981, though I can't competently argue against Rypien.
There are a bunch of noteworthy busts in Redskins history, though Andre Johnson is as good a placeholder in the post-merger era. If we include previous years, that distinction would have to go to Cal Rossi, who burned the Redskins first round picks in both 1946 and 1947. In '46, in the biggest Draft blunder in Redskins history, the team chose Rossi despite that he wasn't actually eligible to play, since he was a Junior (which was the style at the time). The following year the Redskins, clearly enamored of Rossi enough to burn consecutive first round picks on him, chose Cal again. He was so flattered he never played a single down of Professional football, for the Redskins or anyone else.