My wish list goes
Harris
Middleton
Monroe
But I could conceivable be happy with any of the 3. The biggest thing is what DAs moves would be after their acquisition. The front court roster will need to be adjusted based which member of this list is signed.
example
Sign Harris,
He would require the least overall front court change to be effective. I would think that Crowder becomes less of a priority to over pay for as Harris can play the small ball 4. Being an infiror defender I would think Turner would have to be moved and if not Crowder another defensive minded SF (3-D guy) would need to be brought in as his backup. The Bigs could stay Sully, Zeller and KO but eventually a defensive presence must be added.
Sign Middleton,
He may take a J Butler like step up as an offensive option but I tend to think he will be a similar high end role player to AB all be it 6'8. With out a offensive jump the Cs will need to address scoring at the PF and C positions. A motivated and healthy Sully will help but over all Middleton, Sully and Zeller will lack the scoring punch needed from the front court.
Sign Monroe,
This signing would have to be followed by two of the following being traded (KO, Sully, and Zeller. I could actually see a starting combo of Sully and Monroe really excelling on offense but they will need a defensive 3rd big and a + defender at SF as they will struggle defensivly. Though its not going to happen a Middleton, Sully and Monroe front court with Biyombo and Crowder on the bench may be the best pairing of talent.