While both lounges are in the Queens Terminal 2, they’re in different sections and it’s a long walk between the two. In my experience, Lufthansa tends to be busier. It has a self serve bar and the food is fairly good.

Singapore has a buffet and food to order. There’s a bartender. They should still have showers. Air Canada is right next door. United is also close. they both have showers as well. I’d pick Singapore and Air Canada considering your layover.