I love Blake in a vacuum, but his leg injury history, at this young age scares the beejesus out of me.
To lock us in for four years with him is a big risk. Big reward, potentially, but in my opinion not worth the risk compared to other options that may not have as much upside potential, but will substantially improve the team with far less risk.
Hayward, then Milsap are my preferences. Both durable, and Milsap's game will age well as it isn't real reliant on athleticism.
Milsap/Horford would be the perfect mentors for Yabs/Zizic.