The phrase "nice cup" refers to a cup that is attractive or pleasing in some way. It is used to describe a cup that looks good or feels good to hold. Full definition
I enjoyed it very much with nice cup of hot tea. (cookingninja.com)
For instance, a car that has good fuel efficiency (a basic feature) versus a car with nice cup holders (an unnecessary feature). (canadianbusiness.com)
It shakes out to a pretty nice cup of coffee with strawberry jam in it. (gamingtrend.com)