You never know in advance. Book what works best for you based on where you want to go and hope it works with the promo, and if not be flexible.

You make no mention of status or cards you have, but if you can be flexible between P1 and P2 while traveling, you can often times maximize Hilton promos by alternating P1 and P2 nights. For a 3 night stay you book P1 then P2 then P1. You have 3 separate reservations for the same hotel, but dont have to actually check in and out. If its a promo where you get 1,000 points per stay, you get an extra 2,000 points.