I will always enjoy Master Quest the most out of all the seasons. When I watch the first season, I tend to not pay attention because the episodes just don't interest me anymore. Master Quest, however, since it doesn't get praised keeps me interested. Not to mention, the episodes are good, like "Address Unown", "For Ho-Oh The Bells Toll", the Lugia Trio, and of course the Silver League, which had a full six-on-six fight between Ash and Gary.
And Master Quest was the last season of Pokemon that I really had an interest in. Once it ended, I just really didn't want to see any more episodes, and I just didn't care.
D/P looks to be a good season, but I still can't bother to actually sit and watch it. The few episodes that I've seen were good.