um Yusuke is anything but a coward or weak even at the beginning, he just wasn't accustomed to fighting demons. Goku on the other hand is simply just too dense to and probably couldn't tell the difference of a demon from a regular person unlike Yusuke did, that's why he never shows fear. But to answer the question kid Goku is much stronger. He did take on an entire army by himself and tends to beat up cars while Yusuke got run over in the street.
