This depends on what type of striping you want to use. You can control how logical volumes will span physical volumes by an order of LV creation and PV addition. E.g.:
So, now if
lv0 spans whole
lv1 will span
pv1 (in case of linear striping). Filesystem will use blocks first at the beginning of device, so in linear case, if FS spans multiple PV, last PV will only be used if filesystem is full enough.
If you need non-linear striping across fast devices, you may create VG only with these devices. Then create raid LV in it. Then use this LV as PV. I.e. create second level VG from LV. And then add slow device to this second level VG on linear basis.