I love The Mirage as a place to visit while in Vegas. We stayed there in 2004 and had a deluxe room. I was not impressed at all. Small room and in need of updating. Compared to other hotels that I have stayed at, the rooms at The Mirage are the most outdated, and still pretty expensive. The pool is nice, but then again, most of the big resorts have very nice pools.
I suggest staying at MGM Grand. It's HUGE for sure, but the rooms are quite nice and you should be able to find some good deals. Since Mirage, TI, Bellagio, New York New York, and (I believe) Mandalay Bay are all owned by MGM, they are all intertwined in many ways. I'd pick one of those properties. But stay away from Excalibur and Luxor. Nice to see, but too "Circus Circus" for me.