Hello!
The main difference (besides a couple differences in mods) is that the mindcrack pack is designed to be the hardest possible modded experience (adds a TON of complexity/difficulty/challenge/tedium via gregtech).
DW20 pack is designed to his linking, and includes the mods in the unmodified state.
Mindcrack pack also has a couple mods im not familiar with like traincraft and the voxel stuff that could be causing a couple performance issues (dont know for sure tho).
I prefer DW20 because i find gregtech to add a lot of complexity and tedium, but for large servers it might be too easy, with people reaching the end game in a couple days.