Stripe vs sett is personal taste as several people have mentioned. Personally I have never seen a tartan that I do not like pleated to the stripe, yet there are some that look better when pleated to a stripe that is not the dominate stripe. One example of this is Morris of Wales. To me the Morris of Wales tartan looks far better pleated to the yellow stripe in the dark blue field then it does to the white stripe in the yellow dominate striping.

https://www.welsh-tartan.com/tartans/21/morris