OK, I keep going back and forth so I thought I'd bring this up as a topic of discussion. When it comes to Marvel and DC, I collect the gamut when it comes to sizes. I limit the characters I collect (females for Marvel, females and Batman villains for DC) but I have the small stuff like the Infinite Heroes and Marvel Universe and also items as tall as the 13" DC Direct figures, Marvel Icons and even Comiquettes for Marvel. I can't seem to find the right display combinations though. At first I displayed by character, but I didn't like having the larger items with the smaller items. I then went by series/size, but when I did that I got a few characters or lines that only had one or two examples and they seemed disconnected from the rest of the display.
One thing I have determined is that I don't like mixing statues and action figures for the most part. If it's a larger line (like the Women of the DC Universe busts or Marvel Comiquettes) I group them by series, then one-offs or smaller lines I do by character. That seems to work pretty well. I'm trying to get a good balance with figures, try different things out and see what I like, but in the meantime I thought I'd see what other people that collect varying sized figures did.