For me, as a DM, the "sweet spots" are 1st, 3rd, and 5th. 9 times out of 10, if I'm starting a "main" campaign, it's 1st level, no ifs, ands, or buts. (I've got nothing against ECL creatures, monsters, etc., but I like to start out simple.) In 2e I'd sometimes go as high as 2nd lvl, just...