I have heard Xenopus laevis are easy to breed. I have bred Agalychnis callidryas, it was fairly easy, but you will need a rain chamber to do it yourself. See the care article for more details.

The most active frogs are generally the darts and mantellas, but they are not for everyone. They require a little more experience than a White's treefrog does. Barring them, there are the fire-bellied toads. They are colorful, active, and at times comical. They are fairly easy to care for, but the downside is they are mostly wild caught, so they should be treated for gastrointestinal parasites. That will require a trip to the vet.

White's treefrogs are generally considered the ideal beginner's frog. Easy to care for, tolerates handling, CB stock can be easily found, and some what active. If they don't strike your fancy, gray and barking treefrogs make great substitutes for White's, but they are very likely to be WC stock.

In the end, it comes down to what you fancy most and what you are willing to do or learn to keep that particular frog or frogs. I love colorful treefrogs, toads, darts, mantellas, and so on. I find most of what I want comes from Latin America. My favorites are the red-eyed leaf frog, the yellow-eyed leaf frog, Amazon leaf frog, red-spotted treefrog, clown treefrog, Australian red-eyed treefrog, blue-webbed flying frog, bumble bee toad, western green toad, dyeing dart frog, three-striped dart frog, strawberry dart frog, golden mantella, climbing mantella, blue-legged mantella, red-banded rubber frog, tomato frog, reticulated glass frog, Limon giant glass frog, and so on