sort of a tossup IMO. i have had several pairs of the 480s with various capsules, and they have always performed flawlessly with totally professional results. several tracks on various CDs i have produced for RoseWynde (flute/harp duo) were made using the 481s. they are certainly in the same league as my DPA 4011s and schoeps cmc64s. the omni caps are beautifully flat and smooth. their best attribute is high end results at a reasonable cost, if you can find them used.
OTOH, the 8020s are all the rage right now with many pro classical engineers, while the older mkh 20s are not chosen so often - the 8020s offer inconspicuous size for forward mounting, super flat and smooth, great resale value. the 20s and 8020s do have more color than the AKGs, sort of a signature senn sound, which you either like or dont like according to taste. i sold my 20s when i first bought a pair of DPA 4006s.
right now, if i had to choose between those 2, i would say the mkh 20s, but overall, i generally prefer the neumann and DPA sound over both akg and sennheiser. right now, my main studio omnis are DPA 4090s, which i just love, and which also sometimes beat out my km140s as a main pair for chamber work.