[En Sabah Nerd]

I would definitely not call Hot Toys action figures, they're more like investments. Like little, detailed mannequins you buy to display. SH also has big selection limits, they tend to focus on Japanese licenses. They did some Iron Man figures and they're doing some for AoU but only Iron Man hits the mark. They barely do DC either and most of what they do is very stylized.
Diamond Select offers a much more affordable Marvel deal, less pose but more accurate and more selection than SH. DCC is the best way to get DC figures that aren't play-things but they tend to be fragile. Mattel's DC 6" figures are also a popular pick for collectors here, but they do border into the more Marvel Legends like state of kinda collectible and playable. No single Marvel toy line offers selection like Hasbro but you've stated you don't want that stuff.

Hot Toys is 1/6 scale. Pros: really great detail, display oriented, good accessories. Cons: arguably pricey (depending on personal opinion), not actually action figures technically, more space consumed from size.

SH is closer to 6" scale usually. Pros: pose, accessories, size and space taken. Cons: price for size, very limited selection for Marvel and DC, tendency to stylize (dependent on opinion).

Marvel Select is 7" scale. Pros: detail for size, cost, better selection, less space consumption. Cons: limited pose, still not a vast selection.

DC Collectibles is also usually 7" scale but sometimes 6" I think. Pros: good selection, varying styles (comics, games, etc.), size and space. Cons: pose varies from figure to figure sometimes, reportedly fragile (line by line analysis varies).