Which provides the best ROI

I have seen suggestions all over the board concerning the actions used to produce the best ROI. I have seen each action discussed but not comparatively.

Which action, that you use, produces the best ROI?

Is it B2B face to face?
Cold call telemarketing?
Do you purchase targeted lists?
Do you use a dialer or telemarketer?
Are your leads exclusive, shared, live transfer leads?
Do you use direct mail, email, drip mail, post cards?
Do you market a specific area?
Do you market a specific product or provider?

And please post any other actions that you use.

Yellow Pages, local newspapers, association publications?
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