Well considering over the last few years I've sold off a good half of my anime collection, it's pretty clear where I started
Now, assuming I reached a point where I needed to start pruning the games, it would likely go like this:
-All of the Game Gear stuff goes. Not that it's bad, I just play it the least. I mean, I play my Lynx more for cryin' out loud!
-Prune the PS2 & PS4 games. Probably my biggest space-consuming collections, I'm sure there's games in there I don't need to hang onto anymore.
-Re-evaluate boxed cartidge games. Boxes take up space, and I'm not opposed to cart-only- so really, do I need to have any boxed carts at all?
If drastic measures are needed, consider selling/storing older machines in favor of modern clone machines. Even going with FPGA means smaller devices than what I have now- and that's assuming I don't just get a retron 5 & combine a bunch together. Plus, clone machines mean native HDMi, so smaller switchboxes.
Luckily, I'm not in a place where I have to do that just yet.