I've run the Power Enterprise kevlar belt, the HKS true time, and OEM.
Of all the belts I'd say the power enterprise definitely smelled the best, BUT the HKS was extra purple so it's a draw between the two. HKS and Gates are NOT kevlar as many folks misrepresent them to be, it's just high quality HSBN like anything else, and I've *heard* the Evo 9 belt is kevlar backed or whatever but have never seen any documentation that confirms this (smell alone is not enough) soooooo.... Yep.
Oh yeah, and PERSONALLY I'd run all OEM, all the time for any tensioner, tensioner pullys, etc. but that's just me.