bw has most of it right.
QBA is like Bordeaux Superieur, Burgundy Villages, Cotes du Rhone or Mondavi Coastal. They are non-Classified wines, but can be very good. Think Blue Nun.
I agree with bw on these but maybe an easier way of describing them would be(and in the order of increasing cost)
Kabinett- slightly sweet(off-dry)
Spatlese-sweeter, but can go with certain foods
Auslese-Getting towards dessert sweet
BAs & TBAs are Dessert wines similar to Sauternes(Sauvignon Blanc & Semillon) or New World Late Harvest 1/2 bottles with the botrytis smell & taste.
Eiswein(not necessarily sweeter than BAs & TBAs) usually doesn't have the botrytis . Very clean sweet wine.