For me they both serve a different purpose and thus help me equally. Live sparring let's me try things that randomly develop and develop with a resisting partner. Drilling then lets me perfect things, such as getting the right sequence of events down. So sparring gives me the insight into what I need to drill more, and without drilling, sparring is just rolling around trying to force things.
I agree with J-K.
You need both.
You need drilling to get the move down correctly with enough speed, power and balance ..then you can have fun doing it for real to see if you have it and can use it at speed while the other guy is trying to do the same to you.
Every time I see someone that only does live sparring they are sloppy and you know they havent done their homework. They just get in there and start swingin and then get their *** handed to them by the guy that has done his homework and sparring.