All things being close to equal, I prefer to avoid 757s. They're big for a single-aisle aircraft, so it takes forever to board/deplane* and get to the lavs: everyone wants to get there, they're all the way aft, service carts are often in the way, and the cabin crew may object to too many people hanging around waiting their turn.

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*I hate that non-word airline jargon invention, but I don't know of a better one.