I think it depends on whether the horse is buzzy and forward, but safe (my type), or buzzy, forward and bat sh1t crazy with no self preservation (absolutely not my type!).
For me, buzzy would mean the sort of horse who's on their toes, keen, eager to be out and about but not generally likely to do much more than a jog trot
Sharp would be more reactive, potentially explosive, more dramatic behaviour generally
I think of a sharp horse as a reactive horse. This is a good thing (mostly) for a competition horse and doesn’t automatically mean naughty/dangerous …. But can become that in the wrong hands
Buzzy for me is keen, forward, on the go. Good fun.
Sharp for me is on the constant lookout for scary things, on edge and nervy. Anything less than that I would describe as looky. I would describe a well schooled, reactive horse as sharp to the aids, so they aren't sharp themselves and scared of things, but they are responsive.
Quick of the leg is my sort, i.e forward going and quick to respond to the aids.
Sharp to me suggests without any good reason, a propensity to spin on a dime, back up at full speed and possibly leap sideways just for fun. Not my sort of horse.
Oh I like "spicy" - I first heard my niece use it to describe a horse and the way she said it was just so cute! In my head, spicy and buzzy are similar - a keen horse but it doesn't do anything that would cause the rider to come off. Sharp to me means horse can/will try to ditch rider if the wrong buttons are pressed!