Largest flower (if you include petal length as the main determinant, would be paph sanderianum, as in the Guinness Book of Records). If by flower area, I guess would be cattleya lueddemanniana, about 8 inches maximum. Longest lasting flowers would be dendrobium cuthbertsonii, which has individual flowers lasting up to 10 months. I think dendrobium bracteosum is a close second, about 6 months. Fragrance is subjective, some people can detect fragrance better than others.