When you book it will only let you book economy, and you can pay later to upgrade to preferred seating or higher classes. I personally wouldn't bother with it, since when you check in you will immediately get put on the upgrade list for both Delta One and Premium Select. These are positive space upgrades (coded PSUP) which go before any nonrev, and in seniority order if there's more than one, but behind Global Upgrade Certificates (coded UP2W). Since you book them far out it's not really feasible to snipe the airport standby list and take another flight if you see it's not going to work out, you just kind of roll with it. If you don't want to take your chances then sure paying for it is a nice guarantee. I just used mine with my GF to go to Asia and it worked like a charm getting D1 going over, but we got screwed by a last minute UP2W on the way back. Still Premium Select is not a bad ride.