the best veggies are going to be the green leafy ones. the ones like cabbage and kale that are very rough will be tough on your digestion (ever notice you get the kale stomach ache?)
also crufierious veggies like brocolli actually contain indole 3 carbinol (an ingredient in n2guard) and also a potent cancer killer
so i encourage you to stick to that and things like green lettuce, romaine, etc.