I recommend whatever you like best/find most comfortable.
I honestly don't think it matters as long as you get complete, uniform coverage, and so doing what you like best is, IMO, most likely to achieve that. If you something that feels awkward or difficult I think there's a greater chance that you'll get sloppy or otherwise mess something up.
Consider the motions of random orbital polishers, and those work great for LSPs.
The only time I can see the direction mattering is if you get some abrasive contamination stuck between the pad and the paint; then straightline marring will be less obvious than circular marring. But that shouldn't happen anyhow.