As an aeroplane to fly I really like the P-51, it has all the trimming options, a nice, powerful engine, good visibility, it lets me diddle with levers and switches almost to my heart's content.
But as a fighter against ze tchermanz I don't think it stacks up very well, I don't own the 109K4 but to me it looks like the superiour fighter at least for the most part.
But I'll carry on flying the Mustang because I like to.