My ideal is that the cover is like the regular art, but with a little more care and polish because it's a standalone illo that's meant to be looked at for a lot longer than a panel and seen in isolation. So same artist, same pipeline but maybe the inks are neater, the shading is a little more detailed and careful, that kind of thing.
Of course, in Marvel comics it's pretty common, and certainly was even more common in the 2000s, to have a completely different interior and exterior artist. I get the logic behind this, since I'd happily admit I think I'm a better visual storyteller than standalone illustrator, so in some ways it makes sense to have an artist who draws great standalone illustrations do the cover and an artist who does great pages do the interiors... but it always felt wrong to me; there's often little consistency in how the two artists draw the same character, the tone can come across very differently, which is pretty jarring.
I personally wouldn't want somebody to click my work's cover and then for their feeling on seeing the actual interior art to be disappointment or confusion.