Driver without a doubt. I hit it shorter than my 3W (3W goes 230) and it slices like crazy. I know it's mechanics, because other people can hit my driver a mile.
For the last 6-8 rounds, I've left the driver at home and just used the 3W. Doing that has helped me a lot. My all-time low going into this season was 114. Already hit a 101, and have shot 2 47 9's. Man I love golf. The sense of improvement kicks ass. After I figure out how to putt correctly, I plan to work on the driver. But I had 22 putts on my 47 9, so my putter needs a LOT of love.