I’ve gone the route of tallying up all the IPCs (saved and will be collected) and all the prices of the units to figure out a winner, but that’s not all that effective outside of the classic game.
In classic there’s the whole “Magic 84” win for the Axis, but I always hated that one!
A faster route I’ve used before is totallying all the planes, tanks, artillery, battleships and carriers cancelling one out for each side until there’s only one side with some (England has 3 fighters, Germany has 5, means Germany has 2 left after cancelling).  It’s sort of like a “who has more punch” than the other.\
A much more FUN way is to put EVERYTHING on the battle board and fight it out!  Put each side as “attacker” so that a bomber for one isnt massively better than for the other side, of course.
Another way is to declare “Global Thermo-Nuclear War”.  Give everyone 3 rounds to split up, then at conduct combat phase of each turn, you may eliminate all the pieces in a territory of your choosing (Naval or Ground) (NOTE: this occurs AFTER all other combats, but before place new units - and Industrials and AA Guns dont get removed no matter what)