>>10007686Really depends on what you like. But let's have a few safe choices. I assume you already have Marvel Legends, so we can skip those.
McFarlane DC: Armored Darkseid. He's tall but he fits in just about anywhere, be it 6" or 1/18, realistic or cartoony/comic. He's slightly top heavy because his ankles have trouble leaning forward enough, but you can mess with the stability easily enough. He's fairly posable but the character doesn't require high posability. So you can have him posed or just standing there. He lacks an accessory for his Omega Effect but is otherwise a very versatile villain toy.
Hasbro GI Joe Classified: Scales great with ML. Quite articulated and have a lot of accessories. Just about any character is a winner. Cobra Commander himself is perhaps the most limited because of his design, but just about every figure is good because similar to the 1/18 line, they all have the same basic engineering. So it's really a matter of aesthetic preference. Are you in the mood for a Snake Eyes, Spirit, Firefly, Major Budd or Cobra Trooper?
McFarlane: Warhammer 40K Genestealer. Works great as a monster. Even works as a Kaiju as there's a slight Cloverfield resemblance. A unique and versatile toy, the opened mouth and exposed tongue doesn't detract too much because of the monstrous design.
Bandai SIC: Amazons Alpha. Similar to the Genestealer, the monstrous design lets him fit in despite his larger size. Definitely on the tall side if you're looking for a hero though.
Bandai Figuarts: This is a toughie because Figuarts are a tad on the small side. They barely qualify as short Japanese heroes. So go for the Shocker Combatman. He's tall for a Figuarts, so he'll be sufficiently tall for ML and even 7-inchers to a degree, especially since he's a disposable grunt.
Max Factory Figma: Drossel and Scarlet Rain. Don't worry, they're not blood related.