Well, no one would pick the former choice because it's essentially an actual customer base versus stray eyeballs.

But keep in mind that web apps and advertisements are different beasts when it comes to frequency versus reach. For a web app, site, or service - of course you're going to want frequency. When it comes to advertising, the prevailing choice isn't as distinct. I'd contend that reach would have a greater chance of finding potential customers. Frequency can be seen as a nagging effect on deaf ears and blind eyes (the uninterested).