I would have to say Lionel 675/2025 for the simple reason it is the only postwar loco I have in the Lionel range (I have other brands too). However I seem to remember a poll of this type a while back, maybe in some egroup or other, in which the 675/2025 was the winner. So maybe I am fortunate in having the 2025. I do have one other Lionel made after the war, an 8142 from the early days of MPC. This runs fine too and the Sound of Steam
is working well , but the smoke is feeble.