With analog, you have analog artifacts (most notably "sparklies") on weaker signals. With digital, you have digital artifacts (compression noise) which is more noticeable on low bandwidth channels or on transponders carrying plenty of channels.
With digital, the picture won't improve as your signal quality does (for example, a 60 quality signal on a Pansat looks as good as a 99). You either have a viable signal or you don't. Dish and Direct often compress the **** out of their streams, so in many cases, a well-aimed dish picking up an analog signal may yield a better picture than the DBS sats do.