My understanding, from a historical point of view, was that the term "hyper coaster" was coined when Cedar Point built Magnum-XL 200, and referred to a coaster whose height exceeded 200ft.
The terms "giga" and "strata" followed thereafter for the first coaster whose height exceeded 300ft and 400ft respectively.
But then, again thinking historically, these coinages can be argued because at the time the first hyper, giga and strata coasters were built, there were no coasters which had drops longer than 200/300/400ft. So you could easily argue that you take the maximum number of height and drop, and then use the corresponding term.
My main answer is that it doesn't matter. Hyper / giga are just marketing terms to make a big roller coaster sound big. Obviously there's the point that Hixee makes about a hyper B&M coaster, and a B&M hyper coaster, which is a technical term for a product name. But just these number classifications, it doesn't matter to me all that much.
If you asked me to give a definitive answer though, I would go by the maximum height, not the maximum drop.
As a side note, I find it a bit sad that when the marketing people were coming up with a cool name for hyper coaster, they didn't opt to choose a multiplication factor prefix. It would be nice and neat if a 200ft+ coaster was a mega coaster, a 300ft+ a giga coaster, a 400ft+ a tera coaster, 500ft+ a peta coaster, etc etc.