Absolutely no competition Mirage wins by a mile. Flamingo Fab rooms were nothing more than a refresh...paint, carpet , bedding, flat screen. same furniture, bathroom
The GO rooms would be a closer comparison as far as quality goes. And even then I think I'd go with Mirage if price and everything was equal (or within $20 at least). But remember the Mirage charges an extra $25/night that's not mentioned until the final checkout screen. It's collected when you check in and not included in the price you'll pay when you reserve the room. Flamingo and other CET hotels don't have that fee.
In my opinion the mirage is an all around nicer place so while not having any personal experience with either, thats where my vote would go.
Well.....our trip is not until October. As of right now the Mirage is $319 (tax and resort fees included) more than Flamingo for two rooms, Thurs - Sun. I think it might be worth it to pay more. This is a special trip because we are treating our son and his wife to a weekend in Vegas. He just got home from his second deployment over seas and is now returning to civilian life after six years in the Marine Corp.
One more for the Mirage, even @ $319 more. Mirage will feel special, especially if you're headed for the pool. Flamingo, my one time there, was "nice". "OK". "Good place to stay". If you must, walk across the street for some more affordable meals to balance your budget. Next trip when it's not a special event for your son, pick the Flamingo.
May not get you anything, but I wouldn't hesitate to tell the front desk staff at the Mirage about your son returning from overseas. They may be able to upgrade you or something! Worth a shot! Thank you to your son for serving our country!