"Queen's Blade" and "Is It Wrong to Try to Pick Up Girls in a Dungeon?"
I think in this case it is because I've had so many opportunities to get nice merch for these series. While there are other series I might like more (though I like "Is It Wrong to Try to Pick Up Girls in a Dungeon?" and "Queen's Blade" quite a bit, obviously), this is the one where I had the most opportunities to buy quality merch that wasn't some bootleg Redbubble merchandise or something. At the time I was doing Queen's Blade collecting, it was possible to get a lot of quality merch for reasonable prices, I'd probably be screwed if I tried to reproduce my collection today though.
For other series, the merch is mostly books, like for Goblin Slayer or Overlord, and I tend not to count books, manga, DVDs, Blue Rays and the like as merch. For example, there have been a few Overlord figurines I've really liked, but I haven't had the money for them. Oh, I have some Fate and Ranma 1/2 stuff too, but not as much as Queen's Blade or "Is It Wrong to Try to Pick Up Girls in a Dungeon?" (Some day I need to catalogue all this stuff I've collected.)
