If the Wynn is in your budget stay there. It is beautiful! Such a great place. Mandalay Bay is fine but its just far from everything. Also love the Venetian and Bellagio.
We stayed at the Luxor, which was fine for us since we weren't in our hotel much. But If you have a higher budget I would stay at the Venetian, Wynn, Encore, or Bellagio - they are all amazing. I don't know much about Mandalay Bay other than they have the best outdoor beach area. We wanted to go when we stayed at the Luxor which is right next door, but they don't let you in unless you are staying there.
We got married at Mandalay and it's beautiful. THE Hotel there is nice too. Wynn wasn't in our budget, but we'd totally stay there if we could! For a less expensive option, The Mirage is nice too. Really, if you're on the strip, you're in a good spot. :-)
Mandalay Bay is nice but is located at one end of the strip, it's a long walk if you wanted to go the other end. We like to stay at Paris because it's central. Any where you stay you will have fun, it's Vegas!
Wynn is gorgeous but expensive. We got married @ mandalay bay actually and LOVED it, they are the only hotel on the strip with a "Beach". But it is only open from march-oct. If you have the $$$ upgrade to THE Hotel at mandalay bay, so worth it.
Re: going to vegas - ?
Olivia Kate is almost 4!
Diagnosed with autism this year and doing great!