Firstly this should be in the drugs forum, secondly I'm sure there are plently of posts on this topic, or close enough, if you'd just search...
But anyway, enough ranting, here's my opinion:
It depends on quantity and the way the drugs affect you by themselves, and then they can be different when taken together too... For me if I have both I'll have some speed (about 1/4 to 1/2 a point) and then about 2hrs later i'll have a pill (or a cap). This way I get the nice full-of-energy feeling without the aggitatedness a lot of speed gives me, and then the pill kicks in and takes over, but I have quite a bit more energy and can dance for longer than on just a pill alone. If I do it the other way (pill first) I don't really feel the speed, unless I take it as the pill is wearing off, but I still prefer it the other way
------------------
If you're skating on thin ice, then you might as well dance...