I found this great list of the best buffets in Las Vegas on LasVegasRestaurants.com. All the credit and copy-write belong to them so I've copied their list below. I recommend that you go read the full article here and get a detailed review on all the buffets listed below.
"Las Vegas Buffet Guide
The Las Vegas Buffet is an institution. Nearly every resort and casino has its own version of the tour of cuisine known as the buffet. Serving numerous dishes, from soups, salads, and seafood, to international affairs, a trip to Las Vegas seems incomplete without visiting an all-you-can-eat buffet. I recently traveled to Sin City with my boss, in order to suss out which buffets are worth the time and which ones are worth skipping. We begin on a Sunday, with brunch, but for the majority of our stay we focus on breakfast, with some spill over into lunch. To rate the buffets, we utilize a table of 10 categories: Food, Service, Ambience, Selection, Value, Beverages, Wait, Location/Access, Price, and an Overall rating. Each category is worth 10 points. The Total Rating is the sum of these categories. So let’s get on with the show!
1. Cosmopolitan - Wicked Spoon Buffet at the Cosmopolitan 83/100
2. Caesars Palace - Bacchanal Buffet at Caesar's Palace 82/100
3. Bally's - Sterling Brunch 80/100
4. Rio - Carnival World Buffet at Rio 75/100
5. M Resort - Studio B Show Kitchen Buffet at the M Resort 73/100
6. Mandalay Bay - Bayside Buffet at Mandalay Bay 73/100
7. Planet Hollywood - Spice Market Buffet at Planet Hollywood 72/100
8. Mirage - Cravings Buffet at The Mirage 71/100
9. Palms - Bistro Buffet at the Palms 70/100
10. Bellagio - Buffet Bellagio 69/100
11. Wynn / Encore - The Buffet at the Wynn 66/100
12. Aria - The Buffet at ARIA 66/100
13. Paris - Le Village Buffet at Paris Las Vegas 62/100
14. LVH - The Buffet at LVH 61/100
15. MGM Grand - Grand Buffet 61/100
16. Stratosphere - The Buffet at Stratosphere 59/100
17. Monte Carlo - Big Belly Buffet 51/100"