This is a tough one. A pie in the sky question with a bigger picture feel to it. Within this community, I expect Email programs to take the cake - we shall see (someone told me 50% of 'business time' on the computer is spent inside our inbox?).
Looking to see what single factor your company invests the most in to get your marketing messages out there. Results could also vary based on your industry, go to market strategy and your role?
For context on what made me thing of this: I learned that for many companies events is the largest individual tactic by marketing spend and revenue generated. Does it come down to how you track the cost/time spent to enable/optimize these mediums?