Base on personal experience, I have better luck of keeping tetra fish for a longer time. Guppy are easy to keep and breed as well, but are more sensitive to water condition.
Neon Tetra and a transparent tetra (not sure about the name)
algae eater (back) and unindentify fish (front) that came with wild guppies I bought. The unknown fish grew quite big now and it is much more effective in cleaning algae comparing with algae eater fish. It also eat algae that grow on the plants too, but tend to uproot hairgrass.
Close up view of the wild guppies.