well let's look at their abilities as far as i know that is Sonic: supersonic speed, Sharp, durable quills that he can cut/smash when he jumps or somersaults some kind of wind based ranged attack (sonic wind, i'm not making it up he uses it in the multi-player mode of Sonic Adventure 2) a boosting ability that let's him smash through stuff, he can punch/kick stuff and if he has a CHAOS EMERALD he can use chaos control (SA2) and with all of them he can turn into Super Sonic for a while
Rainbow dash: capable of supersonic flight, she seems to be able to smash through barns and things when she's flying and I've seen her smash into the ground with enough force to generate a mushroom cloud ( ANY sufficiently powerful impact can generate one although nuclear explosion are famous for them) beyond that i don't know any other abilities of rainbow dash, although i am pretty sure she'd be a competent fighter
My opinion is sonic would win as he has more combat experience, he fights eggman and other villains almost daily, while rainbow lives a more relaxed lifestyle... as in she's not fighting for her life every two seconds but i could be wrong. reply if you disagree/agree
Rainbow dash grab a ziplock bag full of brown stuff then says"yes my cocane is here"she then uzips the bag greedly and sniff the brown stuff greedly then says and gag"what is this stuff I don't feel anything"then sniffs the brown stuff then says"and this smells horrible".THEN sonic jumps out of a bush and says in arnolds swarchnigers voice"AAARRHH THATS NOT COCANE YOUR SNIFFING A PILE OF DOG SHIT AAARRHH
Sonic: so u think u r faster than me!? RD: hell yeah spike rip off!! Sonic: ''spike rip off!'' Okay then barn animal lets see how fast u r when u r dead! RD: bring it on quill boy! Tails and Twilight: ..... Tails: how many times did he and RD fought over who is faster? Twilight: IT IS OVER 9000!!!!!!!!! Tails: *slaps himself* really really Twilight: tee hee
Sonic: "So you think you are the fastest thing alive!? Think twice! I'M the fastest thing alive!" Rainbow: "IN YOUR DREAMS! You wouldn't keep up with me even if I broke a leg!" Sonic: "Well, I don't think you even need to break a leg! My speed is better! You wouldn't keep up anyway!" Rainbow: "Keep dreaming! I am the fastest thing alive!" Sonic: "I AM!" Rainbow: "That's it! I'm challenging you to a race!" Sonic: "BRING IT, PAL!" Rainbow: "IT. IS. ON!" *background time~* Tails: "Umm, Sonic? We came here for a hangout, not a race." Twilight: "Great, here we go again. Ugh... scary... " Tails: "Man, I'll never hear the end of it now..." Twilight: "Geez, Rainbow! Stop thinking with your wings everytime! You might hurt someone!"
Vector: Hey whats going on here ? Tails: Sonic and Rainbow Dash are having a arguement about who is the fastest. Vector: Let me deal with them Tails: sure help youre self out * in his mind: what an idiot thinks he can stop both of them having an arguement* . Vector * take's in a deep breath and shouts in an scary loud voice *: If you two don't stop argueing right now I'm going to feed you two to the alligators !!!!!! Sonic and Rainbow dash: were sorry and runs off Vector: See Tails and Twilight: Man that was scary as hell
And the funniest part is, that Binky from Discworld is still faster than both of 'em... Sonic and RD can travel at the speed of light and all, but can they travel at the speed of dark? I don't think so >D