I always used to sit in the quiet carriage but gave it up as a bad job because of the number of people who ignored it. Then if I approached the offenders (politely) about it I found I either got a mouthful of abuse or just ignored. Almost worse are the people who leave their mobile ring switched on and then run down the quiet carriage to get to the vestibule shouting "hang on - I'm in the quiet carriage" into the wretched thing.
Better enforcement would help a lot.
So now I sit anywhere in the train and have a hefty pair of enclosed headphones which seems to shut out most of the inane babble that goes on and, I hope, don't disturb anyone else.
Having said that there seems to be a largely mobile dead zone between about Newbury and Taunton so on my usual trains it normally goes pretty quiet. Heading west the signal seems to pick up again just before Somerton Tunnel - shame.