When I used to play years ago I'm sure I remember the advised ruling is that the attacked should get triple to points that the defender gets in a siege to make it a fair fight.

I'm sure I read more recently that it is now double.

Does anyone know for sure what it should be?

Thanks!

There's no fixed number, it depends how you set up the siege, how many ways in, other objectives, etc. 2:1 is probably a good start, but every siege is different.

A numerical advantage of 3 evil to 1 good defender is about right. Played on a large board, the walls should even things out. IMHO.
The larger the point value of the game will benifit the defenders more. A smaller ( 250) coalition of forces will benefit the attacker.