Hi All,
First time here - i've recently inherited a load of MESBG stuff from a friend, including an old 'fellowship of the ring' blue rulebook.

I just wondered, which rulebook is the best? Should i stick with it or trade it out?

A lot depends on what you're looking for.

I think you can have fun with any version of the game. While there have been many detail changes and edge case clarifications over the years, most of the basic mechanisms (order of play, movement, shooting, and combat) have remained recognizable from version to version.

The changes that have been made have generally been to improve the balance between regular troops, magic, and monsters.

So the most recent version of the rules (https://www.warhammer.com/en-US/shop/middle-earth-strategy-battle-game-rules-manual-eng-2024?queryID=b5f64f5e8305435fa42fe17451d8a32d) is probably "best", and of course what most (but not all!) other players expect to be using. You'd also want the most recent Armies of the Lord of the Rings and/or Armies of the Hobbit.

But if you're just looking to have fun with a buddy, you can use whatever rules you want.