First class if I can get it with an upgrade or use FF miles. Not worth the cost to me if I have to buy a ticket.
When I was at Sprint, AMX and Delta had a sweet deal - you got triple miles if you flew 1st class, all our tickets were fully upgradable Y tickets AND they would give you miles even on upgraded flights. This was also when Delta would give you 1000 miles for each leg no matter what. I made a LOT of sweet FF miles and flew a lot of 1st class on that deal
