ChipFlip
Full-tower cases don't get cross-shopped often, mostly because few people need one. If you do, the used market puts the Lian Li O11 Dynamic EVO XL at $149.88 against the Fractal Design Define 7 XL at $135, and they solve opposite problems despite sitting in the same category.
The O11 EVO XL is a display case that happens to cool well
Glass on two sides, a layout built around showing off water cooling, and mounting flexibility that lets you invert the whole motherboard tray. Lian Li designed this for people who will spend as long routing tubing as they will installing parts.
It cools genuinely well too, provided you populate it with fans. Out of the box it ships with none, which is a real cost people forget when comparing prices.
The Define 7 XL is storage and silence
Sound dampening throughout, a closed front, and drive mounting that goes well past what any normal build needs. You can put a lot of spinning disks in this case, which is the actual reason to buy it.
If your use case is a NAS, a home server, or a workstation that needs to be quiet in the same room you work in, nothing about the O11 competes.
The $15 is noise in this decision
At a gap this small the price is irrelevant. Buy the case that matches what the machine is for. Paying $15 less for the wrong shape of case is how you end up rebuying in a year.
Worth checking either way: both are large, and "full tower" is not a standard measurement. Measure your desk or floor space before committing.
Bottom line
Water cooling and a window? The O11 Dynamic EVO XL, and budget for fans on top. Lots of drives, or a machine that needs to stay quiet? The Define 7 XL, and the $15 saved is a bonus rather than a reason.