Kale, Sweet Potato, eat a variety of colors for a variety of nutrients, berries, broccoli, cauliflower, almost all dark leafy greens.

I think healthy works better as a pattern instead of an individual time. Bevi points out that kale etc have the highest ANDI scores and are super sources of lots of good stuff. But each vegetable has its own unique micronutrient profile so, like Maedl says, eat lots of different vegetables most days. How many vegetables you eat most days is the best
marker for a healthy pattern.

My guidelines: variety, moderation, quality. That presumes that you are eating real food, preferably homemade.

But in the long run, I think Maedl is right.

According to the ANDI index, it is kale, collard greens, mustard greens, and watercress. You can read all about the ANDI index here: http://www.wholefoodsmarket.com/healthy-eating/health-starts-here/resources-and-tools/top-ten-andi-scores

Why waste time looking for the healthiEST vegetable? They all have vitamins, minerals, and other good stuff, so eat 'em all.

Chocolate!

Seriously though, I suppose it depends on what specifically you're looking for, like Vitamin A,B,C, etc... There are a lot of different benefits that can come from any one vegetable. It's also good to try and eat as many different colored vegetables as possible!

If you want me to pull an answer out of my butt... Kale is great for you! I eat a ton of it. I even puree it into smoothies :)

John Boehner. Look at all the carotin going on there.