For most characters, I aim for a single definitive version but for some favourites with multiple awesome costumes, I'll pick up the best version of those too.
Iron Man's an easy example, he's had countless suits but I only really like the classic 70s, Silver Centurion, and OG War Machine ones, I don't care about stealth suits or Hulkbusters or even the modular armour. Likewise, I'm never going to pickup every single Spidey suit, just the classic and the symbiote are all I want. I currently have a classic Thor and don't really feel the need for anything else but if a premium version of the Simonson armour shows up, you can bet I'll be right on it. On the other hand, I have a Magneto, Cap and Daredevil that are straight up peak for me and can't see myself ever buying another.
So yeah, basically one most of the time but some characters have two absolute banger versions so I'd want both and ignore any others.
Which means I'm never getting a Polaris until someone does the Maurader version, boo.