Each of the two cars' exhaust sounds are more than able to raise each hair from a bystander's back in its own way, while the tonality is as different between the two as snow is from ice.
Since snow is actually formed by tiny ice particles, while a V8 engine is technically formed by two inline-four cylinder blocks, we could take the comparison further and say that the two types of exhaust sounds are as complementary as are the engines themselves.
In other words, this is not exactly an exhaust battle but more of a concert, with each engine having its own role in the orchestra ensemble, so we can't actually pick a winner. To some, the WRC-like sounds of the CLA 45 AMG are probably more exciting than the rumbling muscle car roar of the SLS AMG GT, while to others it's completely the opposite. Do you guys have a preference?