Well, a digital-switching amp (often called "Class D" by the marketing
types) is inherently more efficient than the traditional Class A/B
design.  Since you're talking about the same power, your results
should sound the same either way, assuming both amps are rated
honestly.  The digital-switching amp will be less of a current drain
on your car's electrical system though.  Typical efficiency for AB
amps is about 50%, whereas you can get 70-90% from a digital-switching
amp.

Scott Gardner

The Class D is is much more efficient.  Their high output efficiency is
in the 70% to 80% range while Class AB is 40% to 50%.  It becomes a
strong advantage in higher power amplifiers.  Class D amps are smaller,
consume less power, and need less cooling.

On the down side, Class D is less common and there are fewer brands.  It
can be harder to shop for them.  Most can only be used for subs but some
are full range.