The twenty words which have cropped up most frequently in advertising slogans over the past twenty years are, in order: you (most popular), your, we, world, best, more, good, better, new, taste, people, our, first, like, don't, most, only, quality, great and choice.
I got that information from a BBC Radio 4 programme called Beanz Meanz Rhymz (to which you can listen again for a few more days here). The programme compared poetry and copywriting. Larry Viner of The Advertising Archives has a huge collection of advertisements dating back decades. He gathered together all the advertising slogans which have appeared over the past twenty years, took out the function words such as 'the', 'and' etc and counted up which words had been used the most.