Hello...I have found that romaine lettuce has the best lasting qualities.
Also it can be found in the organic section. To begin with it has been
treated with much less pesticides, so they isn't as much to get rid of
when cleaning. I wash mine, and then spin dry in a salad spinner. I store
them in that tupperware lettuce holder and they keep for up to a week.
Also, shredded green cabbage makes a good base for a salad. Use in place
of the lettuce and add all other veggies, dressings as you normally would
to a lettuce salad. We do this when we run out of lettuce.
Whenever I buy fresh spinach I know it will go bad fast, so we quick get
a couple nice salads out of it and them I steam up the rest and use it in
a recipe. I use spinach in place of the meat in lasagna recipe.