Crash Team Racing is better.
That's mainly because Mario Kart is physically painful to play. If they let you change the controls so you could use the R button to accelerate then it'd be better, but as long as you have to hurt your thumb holding down the A button it's going to be inferior.
Not sure about Wii U version, but MK8DX has a setting where the kart accelerates itself, you only need to brake (Which I can assure you, it's only actually needed in 200cc and rather infrequently in 150cc).
I'm pretty sure the Wii U version didn't have that. It doesn't really help though, I want to accelerate myself, I just want to use the R button. You know, the default accelerate button in every other racing game on the planet. Why won't they let you just change the controls?