I've read the FAQ thread and have been searching and purusing the threads all morning.  I still have one fundamental question.  How does one determine the best riser-type mount for a flat top upper?

I have a Tasco PDP2 that I wish to mount on my flat top, however I am not sure which route to take.  High rings?  A complete riser assembly?  A combination of the two?  For one thing, I've made a basic measurement and feel that I need to elevate the optic approximately 3/4".  I've seen many rail risers that fit this bill.  But I've also seen many posters' rifles with optics mounted using high scope rings.  Is there a preferred method?

I'd like not to have to buy a half dozen different ring and riser sets just to find a combination that works :)

Thanks.