The best backpacking cup would be the lightest and most versatile. If an item can be used as two or three items you save the weight of the items it replaces.
A lot of backpacking cups are made of ultra light material such as titanium but have double walls so the contents stay hotter longer. A double wall adds to the weight. Some of the best are advertised as weighing only 7 ounces. That is just shy of a half a pound. Besides, if you are cold you may want something to warm your hands. This would reduce the amount of hand warmers you may have to bring.
Another preference when backpacking is how much space an item takes up in the backpack. I have seen and checkout many cups that claim to be the best but take up more room because of a handle that sticks out from the container. A handle that protrudes reduces the nesting capability ( the ability to be stored inside another container such as a pot &$41. Of course you would want a cup that will hold enough of your favorite beverage.
You also want a cup that can be used on a stove or campfire. If you just want to boil some water for tea, why dig out a pan. Also you could also use a cup as a small pot to heat up lunch. What happens if your cup is plastic? Yeah, you have to carry a pot to heat up lunch. Omit the pot and use a steel or titanium cup.And if you travel in bear country you can put a hard item such as a metal spork or a small rock into your metal cup and put them in a stuff sack and hang it outside your pack for a bear warning bell.
Titanium cups can be used on a stove or campfire and weigh next to nothing. The cons about a titanium cup is the price. The more exotic the material an item is made from the higher the price. However, titanium cups can be found in great colors.
Stainless steel cups are a little heavier than titanium but the prices are reasonable. Stainless steel is more rugged than titanium but the sacrifice is the weight. But I don't think half an ounce is that critical unless you are climbing Mt. Denali or Everest.