Well, the sub-solar, visible surface temperature of Jupiter is about 120 K while for Mars it's about 250 K, so Mars would win as the hottest surface of the two, BUT, although Mars has a definite surface, Jupiter just gets denser and denser as you enter its atmosphere, with no rocky surface. Also, the deeper you go within Jupiter, the hotter it gets, with a core temperature of about 56,000K. So, this isn't really a fair comparison because although Mars has a definite surface upon which to measure a temperature, Jupiter does not. You can always find some level within the Jovian atmosphere that is hotter than Mars, but you could never stand on this spot!