My preference these days is to buy a PY-low fare.

The downside (compared to a K-LAT) is that you lose flexibility and refundability - but I'm not convinced the K-LATs are actually that flexible (you need K space for free changes) and if you're ok with a credit then the refund requirement is less critical.

The benefits (compared to a K-LAT): You're guaranteed at least a PY seat, and you're ahead of the entire Y cabin for upgrades.

Everyone needs to make their own choices, but for me the PY model makes more sense these days.