If I'm going to just let people play whatever they want, I don't like either method actually. "The total of your stats must equal 72, nothing under 6 or over 18, (mostly) no racial mods" is what I go with in those situations. It's worth noting that I also use substantial house rules that tend to steer people away from just running 18s and 6s though. Well, most people anyway; the one who did elect to do that turned out to be surprisingly vulnerable and the least happy of the group. I'm not sure how well it would work out in a core game though.
If I'm not going to just let people play whatever, I prefer 4d6 drop lowest, assigned in the order rolled, with the option to scrap the set and start fresh if your net bonus is less than +1. Everyone who has played it with me went into it annoyed, and then wound up extremely happy with their less-than-perfect character after a session or two. I'm not sure if that was because they got over the attribute generation thing or they actually like the occasional undesired flaw, but it hasn't worked out poorly for me yet.