Indeed, I think we're about to see some very interesting times in the next year or so, with regard to GUI/Windowing systems in the Linux world.
Wayland has been a long time coming, and I do hope that's because those working on it are really shooting to get things right. Mir is interesting, and it looks like it will be able to do some things that Wayland/Weston can't, or would require some difficult hacks or even spec changes to make work. I don't know if Mir would be better than Wayland for me, but if you ignore all the FUD from both sides, I think the bottom line is that Mir is better for Canonical's plans unless or until Wayland/Weston can be changed to accommodate their needs.
I personally have no positive or negative opinion on Mir vs. Wayland, but I hope that at least one truly delivers on their potential and shows a clear improvement over our old trusty ;) X11/Xorg.
Not even Ubuntu. They use Mir only as a wrapper around XMir which then displays Unity – they've won nothing with this.
But with Wayland coming to kubuntu this summer and Mir coming to Ubuntu at the same time, we'll see how Wayland and Mir compare in production.