There are many Sunday brunch buffets to choose from while in Vegas and trust me I have been to quite a few. The buffet at the Bellagio is my absolute fav and gets a big gold star! It's difficult to prepare food in mass quantity that still tastes like it was made with love.
On my first round I had a made to order veggie omelet, potatoes, Belgian waffles and the second round I had sushi, pesto mashed potatoes, a few different salads , asparagus and bread! The tea was even great! Make sure you have one of the fresh baked muffins, they are nice and fluffy.
On top of the good food, the atmosphere and staff are great! The price is comparable to most Vegas buffet's. The only downside is the looong line to get in, so go early.