At this stage that Trengrove is a safer bet in that you know what to expect. Naturally Butcher has plenty of development ahead of him at this age. If his relatively poor showing this year came down to injuries, he may yet become a fantastic player.
While Trengrove would be brilliant alongside Lids, Cotch and Collins (in another year or two), it'd be hard to knock back a forward who could potentially dominate games. A forward line including Jack, Butcher, Morton, Nahas and possibly Gilligan? Then include Big V resting up there, and the Postman as another option. That forward line would provide any opposition coach headaches in the future. You WILL NOT be able to keep all of them quiet.
As Bob was saying, mid-fielders are easier to find on a regular basis, so if we don't find one with our second pick (which may go on a solid key defender?), we target one next year (along with a another key defender).
It is really up to Melbourne though as I can't see them passing on both. Whichever is still available at three.