1. Jusuf Nurkic (as of July 6th)
The idea of extending center Jusuf Nurkic is a complicated one. On the one hand, he outperformed all expectations last season and is still only 29-years-old. He has two years remaining on his current deal, that will pay him out a total of $37.5 million. That's less per year than Nikola Vucevic for example, a lovely offensive player but a big with defensive limitations that rival that of Nurkic.
If you add years to the deal now, then it may appeal to other teams to trade for Nurkic down the road because they'd get a big on a reasonably fair deal who can't go anywhere for several years. That kind of control can be nice to have on players four through six on a roster, because it limits the turnover around your star players.
In two years if things remain the same with their top three players - and there's no reason to think they won't - then getting a player of Nurkic's quality on the open market isn't going to happen either. So keeping him in Phoenix as long as possible makes sense for that reason as well.
But on the other hand, Nurkic's playoff limitations were badly exposed by the Timberwolves, and there's only so far the Suns can go if he is a central figure. Beginning next season Nurkic is closer to being an expiring contract with each passing day, which other franchises may look to get in on if it means getting a player they're finished with on similar money off the books. A very tough decision.