Depends what kind of driver you are, if you are not having any issues with fade etc, or wnat to lose as much weight as poss, alloy ones are MUCH lighter than the cast 2wd 4 pots, alloy ones do dissipate the heat a lot better as well better than cast that don't shed heat well.
I'm sure a lot change just for the name, there's a moron round here with massive ap's discs and 6 pots on a 1.1 fiesta!!, rolling on 19" rims spent shed loads on the body stuff as well.
tabetha