Other than some mesclun blends I really like and some red lettuces, I'm not sure I'll ever grow any lettuce than Black Seeded Simpson. It's more nutritious than many lettuces, I never see it in stores (I'm guessing it doesn't store well for shipping), its texture and taste are great, and it's beautiful in the garden.
From Livestrong:
Raw leaf lettuce has concentrations of only two vitamins: vitamins C and A. The vitamin A content of one cup of chopped lettuce is 1456 International Units (IU), while vitamin C content is only 13.44 IU. Green leaf varieties with higher vitamins include Black-Seeded Simpson, Grand Rapids and oak leaf. Red leaf varieties include Red Fire, Red Sails and Ruby. Slicing lettuce before use creates an ascorbic acid oxidase that releases vitamin C, and vitamin C content in lettuce is thus destroyed in preparation by many cooks.
