With gourami, the males are the more colourful, some species considerably so. I always prefer to have male and female, as then you will get more natural and interesting behaviours. As just one example, the "croaking" sounds of the pygmy sparkling gourami will not occur without males as they produce it. All females will not be of much interest, and there is no guarantee they will not be somewhat aggressive anyway. Generally, it is best to have a ration of more female to male, and ensure thee tank is spacious for the species to do this.
All male gourami are territorial, but this does not mean they will tear each other to shreds. The species Trichopodus trichopterus will often be very aggressive, sometimes even to other species; this is a popular fish in stores, and comes in many variants but they are all the same species with the same traits/behaviours: blue, gold, cosby, 3-spot, opaline, marble...common names of the varieties. People often get one or two of these and have them in tanks that are too small, and then wish they hadn't; this species needs lots of room. And even then, careful tankmates; I stood in front of a store tank once and watched as 2-3 of these gourami circled a neon tetra and make a meal of the tetra within seconds.
Given sufficient room, and with a good cover of floating plants and lots of wood and/or plants to break up the space, most other species, at least the small to medium sized fish, tend to be fairly peaceful with male/male squabbles largely show. Though individual fish can vary from the norm. Gourami are not active swimmers, but cruisers, gently floating among plants and wood, so providing an aquascape that gives them lots of "stuff" is more likely to allow a peaceful tank.
The pygmy or sparkling gourami can work in a 30g (113 liter) tank. Length is more important than depth; even though not active swimming (length usually means more active fish), the length gives more space for territories with gourami, just as it does with dwarf cichlids. There is the similar croaking gourami. The eyespot gourami, not common in stores here anyway. The Pearl is a beauty, and quite peaceful, but needs space; at least a 3-foot tank, with one male and two females, or a larger group in a more spacious tank.
