Disclaimer: I'm a huge Mantha fan. I think he's our highest upside player besides Zadina.
Straight up one-for-one? Of course I do the trade. Parayko'd be our best defenseman immediately and is a more valuable piece than Mantha. St. Louis won't accept it though. They'd want Larkin which is a no-go. If we could center the deal around Mantha, it would have to be Mantha++.
Assuming Mantha++ for Parayko is fair, I wouldn't want to do a fair value trade for Parayko. I don't think Parayko's the true #1 we need on the back end and we can get better value trading guys like AA and Nyquist for young, high potential D and hoping they turn into Parayko. Plus I think Mantha has more to show us and his value will increase over the next couple of years. If we were to trade Mantha for a D I'd prefer to do it for a prospect that I think has higher upside than Parayko like the Drouin for Sergachev trade last year.
Commit to the rebuild. Draft, and trade for high potential D and then develop our #1. No need to take shortcuts and move Mantha, one of our big core pieces, for one at this time unless we're getting better value in a one-on-one situation.