I would personally have to say the phoenix worms due to their high calcium. Superworms are like mealworms (correct me if I'm wrong) and have a high fat content compared to nutrition. Their chitin is also not good in large quantities (so I've been told). Superworms (If they are indeed like mealworms) are best given as treats, and no a staple part of their diet. Phoenix worms are lovely however! They also pupate into flies, which chameleons just LOVE chasing around!!
Although, in all honesty, get some of both! A wide variety for your chameleon is always best
Phoenix worms are much better.
As Ferreh88 said, the supers are higher in fat and much lower in calcium.
Other quality feeders include silkworms, hornworms, Dubias and blue bottle flies.
You will find some more useful feeder info here: https://www.chameleonforums.com/care/food/