Cool, how many TFP toys are there (transformers, not masks, puzzles etc.)? My favorite series? Hmmm. I own G1 (movie included),Japanese Headmasters, BW, BM, Energon, Cybertron, Animated sans season 3 (grrrrr >:( ), TFP and movies . . . I watched about a half of RID on youtube (an coincidentally have probably most toys from that series :), and have never seen Armada (but would like to own all of the series). Soo, to answer your question -- probably G1, because it has the longest run/most episodes. But BW, and TFP are probably close second, and third favorites.
Um, no -- I haven't bought any Animated, or TFP figures. Do you? I was always very picky buying toys . . . if it's a good solid design, or I really like something about it, and it's affordable, I'll buy it. Though the last toys i bought were a couple of DOTM figures (deluxe Bee & Dread Suburban + voyager Megatron).