Take the train. It's meaningfully faster than driving, and the time saved usually justifies the price.
You'll arrive about 33m sooner (6h 15m by train vs 6h 48m by car). Tickets start at around £125 compared to roughly £108 in fuel and tolls — so you're paying a bit more, but getting hours of your day back, a city-centre arrival, and the freedom to work or relax instead of drive.
Driving makes more sense if you're travelling as a group (where fuel costs split several ways), want to stop along the way, or need a car once you arrive.