To the OP:
I work for Northern and I enjoy the variance of work, everyday is different in the grand scheme of things. If you want extra money but more mundane work go for LNER, if you want to be paid a decent wage but have much more variance go for Northern.
It’s all relative to yourself. Personally, even with the extra pay, I don’t think LNER would sit well with me, but it may do for you.
Try not to focus too much on the salary aspect, Northern and LNER drivers aren’t a million miles away from each other after taxes.
Good luck