OSX, if you can afford it. There's something to be said for the experience on a closed platform.
That said, if you cannot (or won't) go Apple, then Ubuntu (or some other Debian flavor) generally has the best all-around support for laptops. There's something to be said for an eccentric billionaire supporting your organization with large no-strings-attached checks.
My criteria for good software:
- Does it work?
- Can someone else come in, make a change, and be reasonably certain no bugs were introduced?