it depends on if you like drifting or not.
I don't remember which one has better drift, (i use medium sized bikes,) but the higher the drift is on the kart, the more "tight" it's gonna be, and it's gonna turn faster when you drift.
I use the mach bike with daisy (daisy gives the bikes an extra speed boost). I like how the drifting on the mach bike is.
The Wario bike is much better because it's balanced in all of the bike features. The acceleration is good while the speed is decent and the size or the bike is big too so it makes it a good, all-around bike.