Eat, Drink, Swim....
That's simple enough!!!! Both would probably suffice.... Third World problems! Hahahaha!!!!
As a beach for enjoying, swimming, I would imagine that Seven Mile Beach on Grand Cayman would rate better than Aruba.
I am not sure that either are known for their cuisine and/or drinks. But, I can tell you that eating and drinking can be very expensive on Grand Cayman.
Grand Cayman has the open sand-bar with friendly stingrays, Stingray City, and gorgeous clear blue waters for sailing, snorkeling... (but I am spoiled by snorkeling Puerto Morelos south of Cancun, at the Marine Preserve!)
I might be wrong, but I think a quick comparison would show the main beach area to be more developed on Aruba.
And, it is also known for casinos, etc.
Maybe pretend you are planning a trip to each place... Choose a resort, etc. And then compare pictures, videos.