IMO, you can put players in 4 different tiers for Spurs first round pick:
Tier 1 : Players who won't be available at #20: (13 players)
Wall, Turner, Favors, Cousins, Aminu, Wesley Johnson, Aldrich, Udoh, Monroe, Ed Davis, Patrick Patterson, Henry and Hayward.
Tier 2 : Players who could be available at #20 but also have a good chance of being gone: (10 players)
Motiejunas, Orton, Whiteside, Sanders, George, Babbitt, Damion James, Avery Bradley, James Anderson, Eric Bledsoe.
Tier 3 : Players who should be available at #20 and look like legit options: (10 players)
Alabi, Seraphin, Lawal, Stanley Robinson, Ebanks, Pondexter,
Elli0t Williams, Willie Warren, Armon Johnson, Terrico White
Tier 4: Players that are a reach to be drafted at #20