Europe: Same as the guy above me, I'm yet to do an RMC, so the three European ones are certainly well up there (especially Zadra), but Helix has also been near the top of my bucket list for far too long now
North America: Steel Vengeance, partly because it looks like an awesome ride and partly because it's in Cedar Point, which is pretty much the ultimate bucket list park for me
Asia: Tough one, but I do want to experience that Do-Dodonpa launch at some point in my life, so I'm gonna go with that here
Oceania: DC Rivals, I visited the park only about a month before the ride opened to public (I believe it was just topped of a day or two before my visit), so definitely that. Jet Rescue is also an interesting ride that spited me, but nowhere close DC Rivals
Africa: Tower of Terror
South America: Not many interesting rides down there, huh? I think I always liked the look of Montana Rusa at Parque del Cafe, so I'm gonna go with that, even though I have no real desire to travel to Colombia in the near future