The absolute best live tree you can get to minimize impact to the environment is one that is grown on an organic tree farm or one that remains in a pot so it can be planted after the holidays (if you are in a location where you can keep the tree alive for replanting when the time comes - Minnesota not included).
The absolute best environmental choice of Christmas tree is no tree at all.
(oh, and the above is referring to tree farms and not just running out into the wilds on land you don't own and chopping down a tree, that would hardly be a good eco choice).
What do we do with our tree after Christmas? We put our tree outside in its stand and hang seed ornaments on it for the birds and we don't remove it until the tree is completely dead (brown and dry). Once the tree is obviously dead, which oddly isn't until the end of summer usually (balsams tend to be hardly little suckers after they are cut), we chop it up and use it in our fire place or we'll do something even more cool which I'll share in my next blog post so stay tuned.