I don't know how you feel about the different lines that SSC is focusing on, but I find it difficult to focus on just one or two. As fas as the dioramas go, you have the sentinel 1, wolverine, cap, and both hulk exclusives as far as the heavy hitters. For 1:1s, you have venom and either of the red spideys. In the pf/comiquette line, you have both hulks, both iron man pieces, retro spidey, and depending on your affinity for big, sweaty men in sweatpants, thor and cap.
Personally, I'm kinda torn about collecting PFs...
The Hulk and retro Spiderman are great, imo. I know that some people hate the 'poopy pose' that was chosen for Spiderman, but I have an exclusive stashed away in case I want a Hulk vs. Spidey display down the road. The sweatpant/onsey look that Cap and Thor were given kind of bugs me, but now that I tracked down uncracked Cap heads, the Avengers have assembled... in a pile of boxes.
Personally, I'd get the piece that best represents each character. Also, avoid the completist mentality at all costs and I'm speaking from experience. In all likelihood, you'll never have the space to properly display everything (unless you're squiderm3 or Mesa).
IMO, keep the Cap and IM, even if it means having a sweatpant clad hero.