In a properly built enclosure they are as good as any other speaker in a properly built enclosure. Hell I have even used 18's. It's not the speaker size that makes it sound muddy it's the speaker quality and the enclosure.
Amplifier plays a part in it as well. Amps with very low dampening factors sound like crap. You need to have an amp with >200 at the load you are running for great SQ.
Enclosure> than speaker....... just look at Bose.
Jeff