Which fish is best for small tanks 20 gallon or less?

[Brackishbandit]

Trichogaster leeri (pearl gouramis) 1 pair with a cory , and some danios (long finned ) with some java ferns and maybe amazon sword thats a nice small tank right there sorry I went a little crazy

 

[guppy]

Shelldwellers always make an interesting display, they breed well and their interaction give you a little fishy soap opera.

 

[Lupin]

What is the best centerpiece fish to keep in a 20 gallon or less tank?
Apistos?
Bolivian rams?
Blue/Gold rams?
Dwarf Puffers?

They're fine.

Gouramis?

Depends which species you are talking about. Dwarf gouramis, honey gouramis, thick-lipped gouramis (Colisa labiosa and Colisa fasciata), sparkling gouramis, croaking gouramis, licorice gouramis and chocolate gouramis are fine.

 

[Lupin]

Trichogaster leeri (pearl gouramis) 1 pair with a cory , and some danios (long finned ) with some java ferns and maybe amazon sword thats a nice small tank right there sorry I went a little crazy

In a 20g, danios will easily nipped the gouramis.

 

[reptech]

a pair of hrps or septems.