First fish for a 25 gallon cube

[Rikko]

I assume the tank has mature live rock or you know what you're doing in cycling it. That said, my vote goes for an A. ocellaris. They're tough, pretty, and unlikely to jump. Gobies and blennies are a lot of fun but a lot of the species have a tendency to jump (at least at first).
Chromis? Or just start with a few shrimps?