What is the safest way to store my vinyl records:
Side by side or in piles?
I don’t care about ease of access or collection organization, only about preservation.
They should be stored side-by-side, as vertically as possible, and in an area that doesn't get really hot to prevent warping.
If you stack them on top of each other there is extra pressure on them and over time they warp. Even if they are side-by-side, but are slightly diagonal they are still more likely to warp. Likewise even when kept properly if the area is too hot, warping may still occur.
You can see what warping looks like below: