I stay in all types of Hotels depending on the trip. I looked at your dates December 13-18. The rates are VERY good during that time. This is what I found before taxes and resort fees (usually $30 per night). This is the average per night.

Bally's $39 (Get a high Jubilee Strip View room - very nice)
Monte Carlo $42 (getting run down)
Treasure Island $43
Linq $46
Paris $59
MGM $65 (Avoid the West Wing Rooms - that is the former Marina Hotel - very small rooms)
Mandalay Bay $68
Cosmo $98 (very good rate)

I would either book Bally's (if you want a very nice remodeled Jubilee room for a very good rate) or Cosmo (if you want to splurge at a fantastic hotel with a great rate). The Bally's lobby is fine. It has been remodeled. It is all marble floors and the check- in agent we had was great (just a few days ago).

Upgrades should be easy to get during those dates as Las Vegas is very slow midweek right before Christmas. Some of the shows will be "dark" during that week, some will have a Christmas theme.

You also might want to do a Priceline bid that week for a 5* resort for no more than $70-$80 per night. That does not include taxes, fees or resort fees. If you want to avoid the Trump International state that you want the resort to have a casino (Trump does not). You can select that when bidding.

Good luck! You will have a great time.