I think Sonic would win this. Why? The Sonic Boost. He can do that for a pretty long time, and it instantaneously speeds him up, causing a sonic boom in the process. Rainbow has to dive down for quite some time to achieve this speed and pull off a Sonic Rainboom. Not to mention, Sonic can become Super Sonic, who jogs at Sonic Rainboom speeds
Actually. They don't even know each other. :3 Because they are two different characters from two different shows. Sonic - Sonic X, Sonic The Hedgehog, Sonic Underground, The Adventures of Sonic The Hedgehog, Sonic Boom. RD - MLP, MLP : FIM ... Sonic has 5 shows. o.o
Gonna have to go with my main man, Sonic the Hedgehog. I think the only thing Dash has over him is that she can fly. That could be a problem, but Sonic has proven to be adaptable in the past, so you never know. And btw...I find that little pun in what Sonic said to be painfully funny.