It is all up to you and what YOU want… After all it will be yours to take care of. Do you want a large chameleon that will take a large cage? Or do you want a small tank with plants and a small chameleon inside?
Both are easy to care for, however each has very different requirements. Veild will like it hot, dry and lots of large food, a pygmy will like it cool, humid and lots of small food.
Both are very fun to keep, I like my pygmy chameleons a ton, but I like veilds too… In the end it is all up to you.