I doubt anyone's really gonna agree with me, but while I do prefer Stephanie's performance as Kid Goku, I think Colleen fit better as Gohan.
Now before you throw me those Dumb ratings, here me out. While the performances are generally the same pre-Kai and post-Kai for both characters, Stephanie's raspy voice fit the goofy, dopey, and undeniably boyish Goku better, but the same performance just doesn't seem right to me on the softer, comparatively pacifistic Gohan. For Colleen, I feel the opposite; her softer voice fits Gohan's gentler (at first, anyway) personality, but on Goku it just sounds weird.