Personally, I think the wild colours are the prettiest, but you can get hybrids (crossed with guppies) that have longer tails. You can also get different colour schemes, as it were.
They thrive in harder water with a higher pH, preferably planted. If you go for a mixed group, make sure you have at least 2 females to every male, because the males will otherwise harass the females to death.
I've been wanting a trio or so of these for a while and have owned them before, but since I've been having a hard time finding females around here I haven't gotten any yet. Like bomba, I think the wild coloration is beautiful without mixing any guppy genes in.
My personal opinion would be :
The males fascinating and beautiful but the females are oversized and ugly :( They also breed faster than rabbits...
If you only keep males they could make a fascinating addition to your tank :)
A smaller live bearer is the least killifish (H. formosa). They are however, exponentially less colorful XD