I prefer MW to WaW because WW2 games annoy me.
As for the topic at hand, I enjoy the middleground between the two the most - realistic(ish) setting and actors, but arcadey gameplay - Rainbow Six Vegas 2, Ace Combat 6, Burnout series.
That said if I had to choose one side it would be non realistic. F Zero GX and Super Smash Bros Melee still remain two of my favourite games