I'm surprised at how many people choose piano. As far as percussion instruments go, a piano is quite good I suppose, but I prefer the dynamics of the Marimba...but for sheer dynamic range, breadth of tonality, and expressive modulation there is nothing that can compare with the king of instruments, the Pipe-Organ.
Woodwind - A hard choice, the Oboe would get my vote, but the Saxophone is also excellent.
Bowed instruments; Cello, Viola and Violin are all as good as the player/instrument...never ceases to amaze me how brilliant some players are.
Stringed instruments; The Electric guitar is hard to beat.
Brass; Flugelhorn.