I think a good illustrative example of appearances as relating to style is the Endbringers from Worm, who aren’t the main villains but spend 90% of the story as the biggest known global threat such that even most of the lesser villains sign on with the Endbringer Truce to fight them.
Overall: they’re Kaiju; the smallest is 15 feet tall and they all look wildly inhuman. It’s a long, long time before people work out the significance of this, but the reason is to be scary and intimidating, visibly take damage yet keep coming. Why? So that everyone bands together to fight them, inflict damage and drive them off yet fail to kill them. That is their goal, so they look like monsters you fight that way rather than ones you just run from
Specifics:
Behemoth: The biggest, a hulking horned brute who manipulates energy, throwing lightning bolts, causing earthquakes, incinerating people who get too close. He forces battle by picking a target that the humans can’t afford to let be destroyed (nuclear reactors are a favorite) and just walking in a straight line, impossible to stop.
Leviathan: smaller, sleeker, manipulates water on a grand scale. Fast, and in the water faster than anything. He forces battle by attacking coastal cities; he calls up waves every minute or so and they get progressively stronger until the water pressure tears apart the bedrock
The Simurgh: Smallest; looks like an angel. Precog, grand telepath. She can alter the minds of everyone in a huge radius and sees every possible outcome of her actions over at least several years; she is somewhat impacted by interference from other precogs and fakes being interfered with worse. Apparent strategic commander, picking targets for her brothers and arranging assassinations to disrupt coordination as they attack. She forces battle with her “song”; everyone in range starts getting angrier and more irritable at first, falling to infighting over time. Given half an hour or so she can turn people into long-term sleeper agents; probably only a handful but she’ll sneak them past any test. Standing orders are quarantine the area and kill anyone who tries to leave.
So they’re all very different and each of them has an appearance that reflects their style: Behemoth is tough so he looks tough, Leviathan is fast so he looks fast, the Simurgh decieves and manipulates so her appearance does too. They could look different, but the fact that they look the part clues people in that their goal isn’t pure destruction; they could all just be small invincible spheres if that’s what they wanted. But if they did that then protocol would be to just run and call in people who can kill the invincible and that wouldn’t advance their real goals (we think; the Simurgh has inscrutable additional goals)
On the subtler human side, there’s the duo of Doctor Mother and Contessa. They look like a lab administrator and her secret service agent, basically, because that’s pretty much what they are. In Contessa’s first appearance, she’s in a room with three of the strongest superheroes in the world, all of whom fight Behemoth in close quarters regularly, and she is standing by to extract Doctor Mother if it gets ugly and doesn’t seem worried she might not succeed. They intend to save the world no matter how many crimes against humanity it takes.
The actual main villain spends most of the story not seeming to be a villain and thus purposefully does not look like one; once they make their first overt move their appearance is unchanged but now has a sinister aspect.
Meanwhile the protagonist is running around in dark suits woven from black widow silk with creepy yellow eyeslits because she has bug powers and is bad at telling what people think she looks like, usually the avatar of a vast swarm of insects come to devour all who oppose them. It is a real problem whenever she’s not trying to intimidate people.
EDIT: the deeper point is that there’s not really one best kind of villain. They’re all villains in the same story, they’re all different, and they’re all great. The tone shifts depending on which set is in; “Endbringer Arcs” are basically just a huge multichapter brawl between one Endbringer and over a hundred defenders; Leviathan and Behemoth get tight ones covering the attack itself and the immediate aftermath, The Simurgh’s is much more temporally separated because her attacks aren’t complete until years after she withdraws and is told from the perspective of one of her catspaws. The other villains are fought in a more distributed fashion and often there’s internal conflict between their opponents; unlike the Endbringers their victory won’t obliterate a city and render all conflicts moot, though often there’s a meeting where someone proposes they run the fight on Endbringer Truce rules for bigger threats.
