Different types of campaign can benefit different businesses. The important thing is to identify your requirements so that an informed decision can be made about the most appropriate type to use. For example, e-commerce sites usually do very well with AdWords, whereas businesses that rely on personal branding (such as coaching) tend to work better with SEO.
One of the main differences between is that an AdWords campaign can show very quick results, whereas an SEO campaign can take much longer to come to fruition (six months or more, depending on your site and niche). So although SEO works more like an investment, AdWords can give you some very quick wins. It is also important to note that the benefits of an SEO campaign remain for a time and continue to grow, even after any activity is stopped, whereas once an AdWords campaign is off, it’s off!
Of course, there is always a third way – use both. If you try an AdWords campaign and find that it makes a profit, there is absolutely no reason to stop doing it, even if you are running a successful SEO campaign alongside it. The two can compliment each other well, with AdWords filling in the gaps in keyword coverage that your SEO campaign may be missing, and SEO providing high volumes of essentially free traffic where you need it.