The main difference is are (might not all be listed here):
- Portal gun and Gravity gun (DW20 only)
- Mystcraft (DW20 only)
- Different IC2 solar panel expansion (Compact for DW20 and Advanced for Mindcrack)
- Voxel player (Mindcrack only, makes bubbles above player head when talking and stuff like that)
- Extra bees (Mindcrack only)
- Petrogen (Mindcrack only)
- NEI plugins (DW20 only, not sure why)
The thing is, you can copy the missing mods from DW20 pack into the Mindcrack one (most recent forge version), so you could make the exact list of differences after downloading both and do a merged, and tell your friends what files to copy too.
Do the same for the configs and again for the server mod ad config files, and you will have a full mod pack for now.
I do play in single player like that, and it works like a charm, but do choose between the two "solar", having both is a little overkill, as they basically serve the same purpose.