Praet offers more physicality, more speed and overall is the more versatile player. I'm pretty alone in this, but I don't think Bentancur will be the right player for us.
Bentancur lacks the physicality for B2B and isn't the attacking CM type either. But seems fine as deep lying playmaker.
Praet seems to have it all cept decision-making and "class" (doesn't immediately catch your attn like more gifted footballers) which are interrelated and key. If he's the professional/hardworking/ambitious type, he can grow and become very good under Allegri's tutelage.