If you go with DL, miles don't expire and most DL fares purchased through delta.dumb earn 100% miles (but not necessarily travel agents or consolidators, although there's an Asian exception). As a GM (50,000 status miles required annually, including rollover), you'd have a chance of free upgrades except on elite-heavy routes at business times.

As I see it, the major advantage to picking the KE FF program would be the possibility to use KE miles for IFC award tickets on KE. (DL miles cannot be used for any IFC award ticket or upgrades to IFC.) You would have somewhat more relaxed blackout periods for awards and upgrades than through DL miles.