In my opinion, the player that has improved the most this year is Travis Outlaw.
Travis Outlaw is having a "breakout" season. He has transitioned from a mediocre player at best, to a threat for opposing teams. He never used to play in the 4th quarter, now he is a key for Blazers winning games down the stretch. His consistency is even improving, more than other players on the team in his same situation.
So, which player, from the following group, will be the next to have this type of transition? Or, will none of them amount to much? This is basically the same as asking, who has the most upside? The player may not be in the game for the final 5 minutes, but their consistent contributions off the bench will be critical for the success of the team.