O_O, You are the first Digimon fan I've ever known who actually put season 4 over 3 & 5.
My favorite season is the 3rd season, Tamers. I just felt like Tamers was the most darkest & realistic of the 5, and had the most depth to it as well. I think Tamers just had the best everything in general, the best: plot, characters, writing, animation, etc. I absolutely love the character Jeri Katou & could relate to her battles/struggles with depression as I was going through the same thing during the time of the season's original airing.
Adventure/Zero Two are tied for me, with Zero Two being slightly higher due to that being the first full season of Digimon that I had ever saw. You see originally when Digimon first came on the air I didn't care to watch it because I thought that they were trying to rip-off Pokemon, and ride on the coattails of Pokemon's success. My younger brother gave it a shot though. Then somewhere near the end of the 8th child saga my younger brother had the TV onto Digimon (the episode "Wizardmon's Gift" was playing) & I was in the background playing. I caught a glimpse of it in my eye, and the guy Angel digimon had stood out for me. Then suddenly the cat digimon had evolved, and I turned around & noticed that she had evolved into this beautiful angel. I know this'll sound really strange, but LITERALLY the very moment I had laid eyes on Angewomon I became a fan hooked on this show. I had no idea what the hell was going on plot-wise, all I knew was that I thought that Angewomon was the most beautiful fictional character I've ever laid eyes on & I was happy that the guy angel now had a girlfriend too as well. 3 days after that thanks to my younger brother I was up to speed with the mechanics of the show (digivolution levels, terms, crests, etc.). I watched the entire Dark Masters saga during it's original airing, and had caught the rest of the season during reruns over the summer.