Upgrades are the almost the ONLY reason I fly NWA exclusively. The reason Is I fly a lot of domestic and don't actually go on vacations much. I have over 340K miles banked and not much planned to use them. I almost always get the upgrade (99% of the time). Delta was running about 50%. So I bailed on Delta and fly only NWA.

However, the ability to actually miles to buy tickets is another reason I switched. I was finding it almost impossible to find seats on Delta, for almost any destination, using the lowest miles options. I always had to pay double-miles, to cash in Delta miles. So, this is a close 2nd to upgrades.