One big advantage of dart frogs is that they're active during the day. If you choose one of the species mentioned above, you'd need at least a 15-gal for a pair and that's on the small side. Those species are primarily ground dwellers, so a lower tank with a larger surface area is best. I probably wouldn't keep a pair or group of three of the species above in anything smaller than a 20-gal long aquarium.

A pair of imitators, on the other hand could be kept in a 10-gal with a vertical conversion kit because they use the vertical space and they are quite a bit smaller. However, if you haven't kept dart frogs, the smaller species are not the best to start with and they are more expensive.

Good luck with whatever you choose.