OK

Well we don't run advertising campaigns to associate a slogan with our brand -- I would think that to be an expensive process.

That being said, If I had a well known slogan a domain name of that slogan would seem* to make sense.

But judging buy adwords ...

Keyword Competition Global Monthly Searches Local Monthly Searches
where's the beef Low 18100 12100
we try harder Low 4400 1600
priceless Low 301000 90500

It is costly vanity