I thought I knew the answer to this question pretty immediately: my Albino Drake, of course! It's miraculously summoned from nowhere; you hop on its back, and you fly away! It's magical, so it doesn't need feeding, and you don't have to pay for petrol or insurance or anything like that.
But then I started imagining what it would actually be like, and I think I changed my mind. For starters, if you didn't know, I live in the U.K. That's not an abbreviation of a little-known state, no -- I mean merrie olde England. And, if you hadn't heard, the U.K. is in a bit of a drought at the moment. I'm saying this with my tongue firmly in my cheek, as although we're officially in a drought, this has been the rainiest month since, well, for a really long time. How many flying mounts can you think of with roofs? Yeah.
And flying mounts seem not to have seatbelts of any kind. I don't know about you, but perching atop a magical dragon's shoulders while dodging 747s sounds like something I'd want more safety measures for than my ability to grip with my knees. Also, how fast exactly is 310%? Say I can run at 6 mph. This is purely hypothetical, but let's say that. 310% is 18.6 mph. That's pretty darn slow. Maybe I don't need a seatbelt after all ...
So since I apparently have a preoccupation with travel, I am going to go for a hearthstone. Think about it: You can place it anywhere there's an innkeeper to travel there in a few seconds. Sure, you might need to work your way back to where you came from, but the ability to get home from far-flung places or near to home? Amazing! Or if you have loved ones on distant-ish shores, like I do, you could put it in their local inn and be on their doorstep in moments.
What's your nomination? It could be a spell, an item, a mount, a proc -- anything at all. My only demand is that you also tell me why!