As a non-gamer, I have a bias towards the MO. My last stay at the Wynn was very noisy (thin wall) until we moved to the Wynn Tower Suites.
I have loved all our stays at the MO and the breakfast at MOZen is particularly good. Lunch at MOZen is also good. That said, THE Encore has a much better restaurant selection and the Palazzo is across the Street. At the MO, Crystals and the Aria are a short walk and offer a good selection.
On another front, the MO is a more modern style while the Encore is more traditional. Depends what you like.
While I prefer the MO, the Encore does offer some pluses.