Lecuomelas and azureus are good beginner dart frogs. They are pretty common in the dart trade but rare enough to not find them at your local petsmart. You may have to attend a reptile expo or find a local breeder (which shouldnt be hard).

A few Differences --

Leucomelas - yellow and black, one of the best group dart frogs, loud beautiful call, will use almost every inch of your tank, very bold, and very active.

Azureus - big blue frog, quiet call, should be kept in pairs of one male one female because of high aggression, generally stay on the bottom of the tank, also very bold and active.

Any more questions shoot!

-Kevin