What is better wind milling or stopping the prop on a dead engine emergency landing.?

Cant "stop" a prop. Unless motor siezed.

Just feather it, if variable-pitch. 

I would let it do what it wants, there are more than enough other things I would have to deal with. Looking for a place to land, getting the gear down, dumping fuel, calling for help, etc.

Helicopter, windmilling is better.

Gyrocopter, ditto.

Fixed wing aircraft, varies with type of equipment.

Blimp, not sure.

If you can feather the prop it's better.

If It's a fixed pitch prop it may or may not windmill depending on whether the engine has seized or not.

Stalled prop has less drag than a windmilling prop.

A windmilling prop creates a lot more drag than a stopped prop, so it would be better to have it stop.  However, on most small aircraft the propeller  won't stop windmilling unless you slow the aircraft to near stall speed, where the  glide ratio is poor.  It's a tradeoff... if you're at high  altitude the  glide improvement of the stopped prop may be more than the altitude lost while stopping it an near stall speed.  If you're  low, you're  probably better off letting it continue to windmill.  Letting  it windmill also means it may start again.