757, no question. I have only flown once in F on the domestic 767, in row 1 (I prefer bulkhead rows). Legroom was terrible, and the seats are the narrowest. My preferred seat on the 757 is 1A; with the foot cutout, the legroom is decent for domestic F. You didn't ask, but my favorite domestic F config is the 777, great legroom in row 1 and the widest seats of all.

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Tony