I've stayed in many Marriotts, Courtyards and Fairfields, and IMHO the best soundproofing has to be in the Fairfields.

Take the Marriott Costa Mesa, which I stayed in last night and have stayed in a couple of times before. My first couple of visits I was asked whether I wanted a high floor (>5) or lower floor. Since it was just an overnight stay I picked the level-2 floor. BAD DECISION. The sound from the nearby freeway kept me awake all night, it didn't help that I was facing the freeway.. Last night I got upgraded to a Hospitality Suite. Very night, bed fantastically comfortable, however there was a private function (loud party) going on at the pool (of course closed to the staying guests), and although I was on the 10th floor, the sound was very loud with all windows/doors closed and the air-con on full. Luckily enough the noise died down around 11pm and I dropped off to sleep.

So, my point being is why are so many good quality hotels have lousy (ie no) sound-proofing.

BM