Pretty much all the Anabantoids are single fish. The males of most species are territorial and will certainly chase other Anabantoids, even females of the same species. Some are so aggressive they need to be kept in a tank by themselves.
Over the years I have kept most of the common Gouramis:
3-Spot, several colors, and one male was so pushy he tried to claim all of a 125 gallon (6' long) tank. Only Cichilds were bold enough to stand up to him.
Pearl (OK with 1M + 1F in a 29 gallon)
Moonlight (Original pair was OK, 1M + 1F, but when the F died and I got another he did not accept her)
Dwarf (Single M only)
Honey (1M + 2F)
Snakeskin (1M + 2F in 125 gallon)- these are among the more peaceful of Gouramis.
Betta M separately, F in a group.
All these were in community tanks, but the Anabantoids were the only upper tank fish in their tank. No Hatchets, or similar, and certainly no other Anabantoids. Schooling, lower tank fish, Cories, Loricariads, Loaches and occasionally the more peaceful Cichlids were usually the tank mates. Sparkling Gourami was in a community of small schooling fish, Tetras and Cories.
Currently I have 2 male Bettas in a heavily planted 20 gallon long and they flare a bit once in a while, but they seem to be getting along just fine. Weird! And certainly nothing I would suggest doing deliberately.
Other fish that I have had only 1 or 2 of:
Flying Fox. (Epalzeorhynchos kalopterus)
Siamese Algae Eater (The real one)
Pairs of mated Cichlids like Angels and Rams
Blind Cave Fish
Loricariads: 'Common' Pleco, Bristlenose, Royal, Clown, Candy Stripe, Gold Nugget, Rubberlip, Bulldog and many others.
I often keep my cichlids in singles if I don't want to breed them. Depends on aggression which stay in single or community tanks. Breeding often leads to trouble so if I don't want fry, I keep male only tanks most of the time. It also cuts the risk of having hybrids show up.