The SF Masterworks are a series of previously published books chosen by a publisher. It's not really an award, although they do choose good books IMO.
The
Hugo Award is an award voted by fans.
The
Nebula Award is an award voted by authors.
With the combination of the Hugo, Nebula, Arthur C. Clarke, Philip K. Dick, and Locus awards and their nominations, there are currently 644
distinct titles.