ChipFlip
Case size is one of the few build decisions you can't undo cheaply after the fact. Pick wrong and you're either re-buying a case or living with a build that doesn't fit where you wanted it. Here's what separates the two most common form factors on the used market.
Mini-ITX means real tradeoffs, not just "smaller"
The Cooler Master Elite 110, $55.84 used, is a genuine Mini-ITX tower, small enough to sit on a desk without dominating it. That size comes with real constraints: fewer expansion slots, tighter GPU clearance, and cooling that takes more planning to get right in a space this compact.
Mini-ITX isn't a downgrade so much as a different set of priorities. You're trading expansion room and easy cooling for a footprint that fits places a mid-tower never will.
Mid-tower is still the default for a reason
The Fractal Design Define R5, $99.99 used, represents the more conventional ATX mid-tower path. More airflow options, easier cable management, room for full-size GPUs and multiple drives without creative routing. It's the format most parts are designed around first.
That's not a knock on Mini-ITX. It's just a reminder that "standard" exists for practical reasons, and going smaller means opting out of some of that convenience on purpose.
What actually decides it
Desk space and GPU choice, mostly. A high-end, physically large GPU can be genuinely difficult to fit in some Mini-ITX cases, worth checking clearance specs before buying either the case or the card. If your GPU is mid-range or smaller and desk space is tight, Mini-ITX earns its compromises. If you're running anything flagship-tier or you value easy cable management over a small footprint, mid-tower is the safer default.
Bottom line
Don't buy Mini-ITX just because it looks cleaner in photos. Buy it because you've measured your desk space and confirmed your GPU fits. Otherwise, the extra $44 for a mid-tower buys you a build that's easier to live with.