The key to success with veggies is variety. There is no one super veggie that does everything, so mix it up and choose what looks fresh. Very few are "bad" for dragons on an occasional basis.
Our normal go to list includes :
Collard Greens, Turnip Greens, Dandelion Greens, Mustard Greens, Kale, Chard, Bok Choy Parsley and Cilantro.
Zucchini, Yellow Squash, Shredded carrots and bean sprouts.
Stay away from most lettuces, as they are mostly water with no nutritional value. A little here and there is ok, but don't make it a mainstay.
Avoid spinach, as it binds up calcium in most reptiles.
Berries are a good add on, but more messy, so use in moderation.
Veggies alone will not contain enough calcium nor vitamins, so add a high quality supplement to them, We use and Recommend Repashy Super Veggie. It is formulated to boost and balance the nutritional values of vegetables, and sticks to the veggies well.