Numerically and emotionally there's a very strong case for the Tiger, but it was primarily a military aircraft that fell into common civilian use post-war because they were plentiful and cheap. I'd have to vote for the D.H.60 Moth, Geoffrey de Havilland's 'Aeroplane for All' (though it was never truly that for private flying and aircraft ownership never were and never will be cheap), the first truly practical British light aeroplane, happily well represented in several variants on the vintage scene. Having said that, I reserve the right to make further representations when I've had more time to think about it! Something Miles has to be up there, I feel, as Hairyplane will no doubt point out.