What I've always heard is that Skiff is more oriental heavy, vs SL which is pretty much virginia and latakia. I prefer Skiff personally--the tangy bbq oriental keeps it tasting fuller and more interesting.
Bulk isn't sealed, so you lose some aroma/flavor. Most of the time, since these sell quickly, it doesn't matter all that much.
I don't buy things like ennerdale or 1792 in bulk anymore though.
I'd recommend carter hall. It's very forgiving. I tried starting with virginia flakes and hated it. Carter Hall let me get the mechanics of pipe smoking down.