Well theres tons of threads, but the main point here is...

Anything above medium battles makes the AI VERY powerful...and anything above medium campaign makes em kinda kooky and have a powerful fetish for destruction of whatever you wanna call an empire.

I used to play VH/VH....till I got bored out of my mind killing 3 stacks of uber stat units with a single stack that couldnt be replenished....then it was like oh crap here come another 5 stacks...screw this lol

M/M is probably the best, it gives you choices and keeps everything nice and tidy.

Of course you can always opt for medium battles and harder campaigns, but thats your thing, just keep it to medium battles