I go straight up and down. If the whole blade fits on the strop, awesome. If not, I move the razor a bit between strokes to ensure that the whole edge gets a fair amount of time on the strop. I guess that ends up giving all parts of the razor a good amount of strop time, but the middle will still get more than the toe and the heal.

To be honest, I place far more emphasis and effort on honing and shaving technique than stropping. If a blade is poorly honed or if shaving technique is bad, amazing stropping won't help. But getting good at stropping is not difficult, and I'd have to imagine good stropping vs spectacular stropping will have some seriously diminishing returns.