How do you determine which marketing channels work best for any given feature rollout?

We understand what marketing channels work best for a feature rollout by talking to our customer. Everything we do always comes back to understanding the customer better than anyone else in the company. 

For example, if I talk to a customer and I ask them why they haven't enabled a specific feature, I would ask them how would they like to learn about new features. I'd run surveys, focus groups, and A/B testing to determine the most effective communication strategy to ensure customers adopot our features.

SaaS companies should also not over look using utilization reports to segment their customer base and then run in app campaigns to highlight new features. The is especially true if adoption of that feature will lead to upsell or cross sell opportunities at a later point in the customer lifecycle.