Good Frogs for a 20g Long Tank

[Mentat]

A baby Pacman will just need a critter keeper like the ExoTerra medium Breeding Box. Only when it reaches 3-3.5 in. can you move it to a 10G.

A large female Ornate or the rare Aurita can eventually exceed that tank size and require a 15 (or 20H); but even then, rarely a 20L .

[CinnamonPearl]

Right now, I'm choosing between a pacman frogs, mantella frogs, and bumble bee toads. I'm especially interested in mantella frogs. What species of mantella would you recommend for someone who's a beginner to them?