Trainline is a fairly typical commercial website. It won't work without javascript and cookies enabled, it wants to track you, it doesn't follow accessibility guidelines and is over a megabyte and a half in size. If you access it on a mobile device it has the usual annoying ad for the pointless mobile app (complete with onerous Ts & Cs, overly grasping permissions and invasive privacy policy) covering a quarter of the screen with the tiny dismiss button. In short, everything that's wrong with web development these days and defensible only because it's one of many.

By contrast traintimes.org.uk is simple, highly usable, small, accessible, respectful of privacy and works as plain html.

For me it's an easy choice but your mileage may vary!