This kind of cutting of the groups will always give you problems on a skirt, there is no ideal way of conforming skirts but only workarounds. The morph way is IMHO the best way to go, it is a little bit more work for the modeller, and you need to adjust the morphs when you pose but you can get a smooth animation from standing up to sitting that way. I leave the abdomen part as standard conforming but the hip is driven by morphs.

Dominique Digital Cats Media