We've upgrade before and it's Delta Comfort. You get extra leg room plus other amenities but to me it wasn't worth $149 pp Outbound one way this trip. In the past it was $49 which was well worth the pre boarding, extra leg room, cocktail, upgraded snacks, blanket, etc. Inbound Delta comfort one way pp this trip is $79. Forgot to add you get one free checked bag with Comfort class.

Just my 2 cents.