i never had a problem with the 456 lines, and I used them for 6+ years before moving to W'Burg. They're not perfect, but if there's was a problem with one line, I'd just take the other. Rarely would all the lines be down, though it has happened and this is certainly a pain.
the upside to the 456 is consistency - waits over 5 minutes were always rare, even late nights. I find that the West Side lines are tricky when it comes to consistency even though there's many more lines .. I've been stuck on the A/C platform for a while before. I've also wound up way uptown on a train that went right from 59 to 125 (why wouldn't you stop on the UWS???).
We are very lucky when it comes to general people sounds ... to one of our walls is an exterior wall, the other is structural, one faces the yard with windows, and the hallway wall is damn thick and has a sound killing vestibule for the front door.
and we have neighbors who don't give a shit about noise I make. As long as they don't give my dog some of their coke, we're all good with whatever.