My top picks for buffets were:The South Coast Casino;Village Seafood buffet at the Rio and if you happen to like gospel music...I mean that down home ass kickin stuff right out of church,I HIGHLY RECOMMEND the Gospel Brunch Buffet which happens every Sunday morning and early afternoon at the HOUSE OF BLUES at the Mandalay Bay Casino.
The food there was out of this world and you get the show and the buffet for $35.00 with a coupon.
If you have access to a car and are into great food at great prices I would also try Paymon's Mediterranean Grill on West Sahara;Thai Spice which is close to the Rio and Sababas on South Durango.Unbelievable food at all 3 places but you do need a car.
Stay away from Circus Circus buffets.Not great.
The Wynn also has a great buffet but it is expensive.
Hope this helps you,but even if it does not help you...locals...take my word for it.These places are great!
Here is the link for the House of Blues brunch.You will not be sorry