The Lizard Men
Nemesis: Martian Manhunter
Other Major Foes: JSA
Appearances: 3 comics.
Powers: Super-strength, durability, invulnerability to fire and mild chameleonic shapeshifting. Wear body armor, carry specialized flame throwers, and handle powerful saurian "lizard-dogs."
Bio: The Lizard Men were the soldiers of the Master Gardener, and conquered Earth for several years in the 1950s thanks to a fungus they introduced to infect most of the global population. They were routed by the Martian Manhunter, with the help of Dr. Mid-Nite, Bill Gaines, Fidel Castro, Elvis Presley, Che Guevara and/or reasonably facsimiles of same.
Win: Thythen (10-4), The Martian Marauders (5-4)
Lose: VULTURE (8-10); B'enn B'urnzz (?), Thantos (?)
Nemesis: The Titans
Other Major Foes: The Omega Men
Appearances: 25+ comics and appearances in animated series.
Powers: Enhanced strength and durability. Wear body armor, carry energy batons, and possess advanced alien technology.
Bio: The Gordanians were the soldiers of the Citadel, and conquered worlds through their warrior culture and slavery. They were routed at various points by heroic super-teams, with the Tamaranean ex-slave Starfire being something of a constant.
Both of these guys are scaly thug armies-- the space opera equivalent of the nameless muscle behind Kobra/Hydra/etc. The Gordanians are more Jem'Hadar to the Lizard Men's Cardassians, and if you got those references, congratulations on being a total nerd. I never liked the Gordanians, both because they're scummy and because Marv Wolfman wasn't good enough at sci-fi to overcome my hatred of Starfire the way he excelled at horror that overcame my dislike of Raven. The Lizard Men seem to be out-gunned as a whole in a big way, but they came across as more sly individually. If you took a party of Lizard Men with their "dogs" and sicced them on a given group of Gordanians, I'd say it's a toss-up.