To put it simply: Mindcrack is hard mode (difficult IC2 recipes/no instant teleportation or lossless transmutation)
In more detail;
Mindcrack has a lot of advanced tech, processing and power options- a little reward for conquering the hard mode. (methane boilers, lava can be processed into any base metal)
Direpack offers a few neat features that make life a little easier (instant teleportation/on hand crafting table)
As general mod play goes- there isn't too much of a difference.
Generally- if you're new, go Direpack
-if you like a challenge to Mindcrack