I voted 1-10 or so. Those are the levels I enjoy playing and DMing most. I like the gritty, more realistic feeling of the low levels (1-3), where almost any threat can become dangerous, and the competent, but not godlike mid levels (4-8 or so) where the characters can hold their own, but still have to worry about mundane foes. Higher levels (9+) quickly begin to lose their appeal to me- the game becomes too complex, and the characters become godlike with superhero-like powers. Plus, its really hard to challenge the characters without using bizzarre monsters, outsiders, undead, or templated creatures- and how many of those realisticly roam around? The game just falls apart IME at high levels, both ruleswise and in terms of consistency. I want the PCs to be people who exist in a world, not above and beyond it.