Since I don't really feel like leveling a character on each server just to get a better idea of the differences, I'm wondering if someone could give me a tl;dr about what the key differences are between those servers.

Anyone have any experience with it?

PoD - Modified 1.13c
PD2 - Modified 1.13c

Both have differences but are equally similar at the same time. PD2 has just launched, PoD has been around for a few years.

Slash - Vanilla 1.13c with quality of life improvements