This is definitely a hard thread to post in, simply because I only own two species of frogs currently but I love all kinds, even those I have had no experience with.

I'd have to say that White's are my favorite. Bruce Campbell, my first frog, is a White's and I don't regret the decision to start off easy. White's have great personalities and are great beginner frogs. Also, their ability to be handled more often than other frogs has to be a plus, though you still have to take it easy I love to be able to hold them for brief periods of time without worrying that I'll hurt them in some way. It's a lot easier to connect with an animal when you can hold them in your hands. Another thing I like about White's is their wide range of colors. I know usually they're restricted to just the basic brown, green, and blue, but I've seen White's range from yellow, to orange, to purple, to almost black. Having a variety of them in one tank should be a fun experience.

Although I don't own darts I'd have to say I already have a favorite, and it's solely based on the visual aspect, but whatever. XD R. vanzolinii have to be my favorite darts, just because of their amazing coloration.