If you just want the ETO theatre and plane-set then use EAW1.2, the new GoG release, or EAWPro.

If you want multiple theatres with their own plane-sets then use 1.28E, 1.28F, 1.29, or UAW140.
If you want a system with multiple theatres, and multiple plane-sets which are independent of the theatres then use UAW160.

UAW160 is the most flexible as you can still select the default ETO theatre and the default ETO plane-set to fly careers, or do something crazy for sheer entertainment and fly in the Finland-Russia theatre with a Pacific plane-set

There is also 1.28c, but organising planesets is trickier.
There is a patch for the GoG release that gives you a good selection of theatres

Just wanted to say to anyone with the GoG version of the game. Mr Jelly,s OAW 160 patch works a treat, it’s incredibly easy to install and set up every new theatre etc loaded is just a few clicks and your in. Fantastic work Jel.