Before looking into Gobert more, I would have said Gobert. He is so tantalizing on paper, with his 7 plus height and unreal wingspan of 7'9, plus he looked pretty mobile in highlights. After getting a more extensive look at him and seeing his stats, I'm not too impressed.
First off, he's kind of stiff. His lateral movement is poor and he doesn't get much lift. His stats bore that out. One thing I didn't realize is that he plays a lot of minutes. I figured he was on the typical youngster timeline in European basketball, not getting many meaningful minutes. I was wrong. For instance, in his last five games, he's played 24, 27, 21, 24 and 30 minutes. Thats' a good-size amount over in Europe. In those five games, he's averaged 4.6 rebounds and 1.2 blocks a game. That comes out to 7.3 rebounds and 1.9 blocks per 40 minutes. For the season, his rebounds per 40 are under 10, which is a poor translation from Europe to the NBA while his blocks per 40 is good at 3.5. If he's a poor rebounder and below-average athlete, I'm not sure he's that good of a prospect even with his freakish size.
I wouldn't mind if Ainge passed on Olynyk, Gobert and Austin.