Blimey klambert, that's a good question.....There's so many different choices.
Of all the UK routes, I think Angela's WCL 1 ( London Paddington to Reading ) is probably my favourite as I used to work at Paddington, about 22 years ago, and it brings back fond personal memories of the area, and it was such a great line to travel on and she's done a fabulous job of recreating it.
Locomotive wise, all the major classes of BR Blue diesels are superb.
However, being a complete Trainz nut, I like many of the routes from around the world and their locomotives to match....
Cheerz. ex-railwayman. :wave: