Personally, I'd prefer to keep the existing accepted answer pinned behavior.
The primary reason for this is that it's quite common for someone to post a superior answer after others have already attracted upvotes. Under the newly-proposed system where accepted answers aren't pinned, the new, better answer would often languish in obscurity beneath possibly several answers that were posted sooner and already had some upvotes.
This effect is especially strong when a good answer is posted more than a couple of days after the question was posted. The person who posted the question will get a notification when the new answer is posted - and possibly choose to change the accepted answer if they think it's better - but most others would never see it if there were already at least a few other answers with some upvotes, even if only a few. This is not helped by the fact that questions tend to get a lot more visibility soon after they are posted.
By moving the accepted answer to the top, the later answer is pulled out of obscurity at the bottom to a position where it's much more likely to be seen (and voted on) by others.
The worst that can happen with the current (accepted answer pinned) behavior is that one lower-voted answer appears above the others, while the remainder remain sorted by votes. Whereas the worst that can happen by unpinning is that the best answer is hidden under a pile of answers that aren't quite as helpful, but were posted earlier.
What I'd really like to see is an option to pin the accepted answer above all answers that are older than it, but, unfortunately, that's not one of our options here, so I think that maintaining the current behavior of accepted answers being pinned is the best of the two options presently available to us. Hopefully SE will come up with a better sorting algorithm that takes age of votes into account later on. Possibly they will come up with something better in 6 to 8 weeks.