I use the c2c line, and whilst today is an unfortunate day to ask this question as they had chaos due to power line failure, they are a brilliantly run line. 95%+ punctuality, modern clean trains, good value vs other SE lines, loads of trains per hour. Couldn't be happier.
Was on a Virgin train from London to Birmingham at the weekend and that was also excellent; I've traveled that line tens of times over the years and rarely had a problem. Super quick too.
However, I know that other parts of the country fare much worse.
But I certainly wouldn't want my line re-nationalised. You wonder why the govt doesn't get the best lines to take over more of the poorer lines, the way TFL has been doing with the East Anglia routes.