Wasn't Base Set 2 released as a filler since there was a long delay between Fossil & Rocket? If I recall correctly, Fossil was released in October 1999 (wow) and Base Set 2 was released as a filler set in February 2000, before Rocket was released in mid-April. And then there was a quick acceleration, as Gym 1 came out in July, Gym 2 in September, and Neo 1 in December.
Ever since then, though, I think the release schedules have become much more regular.
My least favorite set is Supreme Victors. Although there are some good scattered cards in the set, most of the set is horribly under-powered, and almost all the good cards are rares or holos. And with a significantly larger number of cards than other recent sets, you were a lot more likely to pull undesired cards.