+3
Interesting question. When I think of either of them, it's more like old Hollywood icons than as actors. As actors neither of them morph into a character, both are Stewart or Grant putting on a costume and adopting dialog. It's THEM that was the character. I think, back then, people expected that more than a chameleon-like actor. It's like how John Wayne was always John Wayne.
Personally, I preferred Jimmy Stewart's gangling look and staccato speech more than Grant's mild British speech. Stewart had more of an everyman demeanor and nobody would describe him as being suave.
The Rear Window is really a favorite of mine, Stewart doing his usual character, but this time with a broken leg and a camera.