No brainer for me . . . Lockheed P-38 Lightning, either an F or an L. What I'd really like is the XP-38, but it's in a million pieces, so I guess that's out of the question.
Second choice (unless I get two choices!), would be an Me-262, either an original (highly unlikely), or one of the repro's from Stormbirds up in Washington state (though I think all five airframes are already spoken for).