I have researched the shops in my area and none offer the jumbo size, just standard and mini, maybe it is an American thing.
We also don't offer jumbo cupcakes, only regular and mini. We were initially planning to offer jumbo cupcakes but most people want either regular cupcakes (1 cupcake per serving) or minis (about 3 per serving). Jumbo cupcakes are more than 1 serving and are awkward to divide up.
Mine are in the middle. I use tulip liners. They are bigger than regular and still one serving.
Thanks ladies! I think that has helped make my decision, I may offer jumbo muffins though.