I assume that this will be you first pygmy chameleons...
If Yes, I recommend you to start with Rieppeleon brevicaudatus.
They are cheap and the best pygmy to start with(my oppinion), because you can keep them almost in any enclousure and they are easy to keep and breed.
Other species such as Rhampholeon spinosus or acuminatus are more difficult to keep and breed, because they need a good night drop and you must also watch the daily temperature, the daily temperature by this species may not exceed the 22°C(my oppinion and experiences).