Ah, yes. Mexicana is probably the most invasive water lily. I had a bunch, but got rid of them because they aren't the best of bloomers and if you let them will grow inside of other pots if you let em!
For me, the hardiest would have to be daubin. It makes so many plants, and if you know what you are doing, you can grow them in just about anything that will hold water. It's also a terrific bloomer.
