Taurmindo said:
i play it myself with three investigators a lot, mostly to test-implement house rules or expansion-combos. the win statistics is highest when either we're three players with one investigator each, me with three investigators or two players with two investigators each. adding players and/or investigators quickly reduces win chance. in my group. but it's a special group.
I usually do 4 investigators, because it's on the "verge" of two things: 1 monster per gate instead of 2, and 7 open gates instead of 6. Having 3 investigators has the same rules, but with 1 less person, so that's why I play with 4, and why I'm sure so many call it the "sweet spot." Though I also houserule that when I play with 4 (because sometimes, depending on how many investigators are devoured before the AO wakes up, and how late in the game), 2 monsters come out of the first gate (and first gate opening only), to help get things moving!