I work partially in German and I think that I often hear "hoch wahrscheinlich". I looked in a dictionary and it seams that it is better to use höchstwahrscheinlich. Google also translates "very likely" as "sehr wahrscheinlich", which I feel is less often used. Could someone comment on the difference between the three phrases? And also which ones are more authentic/grammatically right?
In everyday speech, you'll probably only hear "höchstwahrscheinlich" and "sehr wahrscheinlich". "Hoch wahrscheinlich" sounds like jargon from some (maybe technical and/or scientific) field, where the exact difference between "höchstwahrscheinlich" and "hoch wahrscheinlich" is definied and relevant.
In general, it's mostly a matter of degree. "Sehr wahrscheinlich" literally means "very probable" or "very likely", "hoch wahrscheinlich" means "highly probable" and "höchstwahrscheinlich" means "of the highest probability" ("highest-ly probable" doesn't compute in English ;) ). So the order would be
"sehr wahrscheinlich" < "hoch wahrscheinlich" < "höchstwahrscheinlich"
But don't be surprised if this more technical distinction isn't always followed in everday speech.