So long as the intent is to allow people to make better decisions about what distribution to use, instead of simply to switch as many people as possible to using Debian.
We do not want to switch people if they're better off using some other distribution, and nor do we wish to waste effort switching someone who is equally well off whether they use Debian or some other distribution. The most beneficial way is to write an article (which you don't even have to pay LJ for!) that tries to direct each reader to the distribution that's best for them. By being one-sided, advertisements have a higher tendency to direct people _away_ from what's best for them; and are also less credible. However, an ad may be beneficial in redressing imbalance in image portrayal if such an imbalance exists. pjm.