personally i don't think it makes a big difference which slip-on and header you use for every day riding. reason being, i haven't seen any info putting one way out above the rest!
but of course, with each kind of riding you do, there willl be a better pipe! that is if you want more bottem end, mid range or top end!
only someone who put in the extra time tweekin his/her bike will get a little more hp out of the slip-on and header
so that is my 2 cent