After watching Civil War, holy crap definitely Iron Man. Breathtaking performance by RDJ and he was basically given some of the most heartwrenching moments in the film.
Though this is definitely a Cap film, it can easily be argued that this is also an Iron Man sequel film, only with Tony as a sympathetic protagonist/antagonist. There's this dangling plot thread left in TWS that CW really uses to full effect as means for framing Tony's character arc and it's just terribly depressing that I couldn't help but feel so bad for him throughout the film. This is definitely one of the biggest turning point for Tony's character and I'd say that the Mark 46 will serve as a definitive Iron Man suit for many people even after everything is said and done with how great his portrayal was in the film.
Beyond that, I'll also be getting Cap since I've always wanted a figure of him, and he was also outstanding in the film. I might get Crossbones for the cool factor because he felt like a beast and actually served a key role in the film, small as it was. Zemo would have been great since I feel like he was actually brilliantly handled, but the fact that he doesn't really have a proper villain design is the only thing that makes it unlikely for HT to even consider making him.
Now honestly, unless you're a completist or if you love the idea of first appearances, I think it's best to wait for the solo Black Panther and Spidey films for their respective figures especially if you're the type who would rather budget and carefully choose your purchases with each character. For Black Panther specifically, the figure feels really lacking without an unmasked head sculpt, especially since he takes it off a couple of times in the film.