What online marketing works best?

Only a very few businesses can take the form of having only a 100% online marketing strategy. Usually these are net server providers, domain registrars and online web tools and applications.
Net server providers host your web content in their server so that your website can be widely appreciated by all. Examples are go daddy, Rackspace, hostgator, network solutions to name a few
Domain registrars accommodate registering a domain name.

Most servers allow domain registration as well. They usually have package hosting plans.
Web tools , web services and applications can be anything from the services of Google, Yahoo, Facebook to Skype. Web services like Social media, Seo and web designs are also 100% sellable online.
These types of businesses facilitate online activities and so marketing online to direct consumers makes a lot of sense. They can be a 100% online marketing company due to the nature of their services, theres a perfect match for the buyers and the sellers online than anywhere else.
The best channels for these types of businesses are Pay per click, AdSense, social media and Seo.
Target -> Online Community

Some businesses however rely on a higher online marketing mix than its offline counterpart. Both are treated as extremely important but online marketing take most of the effort, time and money. These businesses can be real estate businesses, event organizers, specialization clinics, drop-ship merchandising and professional services like photography or catering. These businesses need to attract people of all demographics, orientation and income brackets. The market is definitely big and it need a lot of strategies to cater to different types of people. However, the trick is to be able to find a niche to be able to market more productively. Usually a newly formed business sticks to this form as their primary marketing drive due to the low costs involved in internet marketing.
For these businesses – Classifieds, Seo, email marketing, video marketing and social media are great tools.
Target -> Niche Markets

There are businesses that require a lower level of internet marketing but need to focus more on offline marketing. These businesses are already well established, already have a steady customer base and may already be a big brand in print and TV. They use the internet not more-so to market to newer clients but to facilitate better and faster customer relations and  purchasing systems online for existing clients. They usually provide more online services to customers. Banks, schools, NGOs, hospitals, and famous brands typically comprise of this group. These businesses are more focused in having their internet community well informed and want to share environmental concerns or philanthropies with them. Over the years a huge distrust has developed between consumer communities’ and the corporations, social media brings in a harmonious balance since the companies want to be able to show their good faith and customers want to hear about them giving back to the society.
Social media and Press releases are very important for these businesses.
Target -> Mass

The truth of the matter is that at one point a business may start out as a niche marketing company and then head somewhere else. The best online marketing option for your business, company or corporation would rely heavily on how your business logic works. If the logic is correct then, finding the correct online marketing activities would be much easier and simply more logical. On founded reason, your business, company or corporation would be able to market more effectively and be able to look past the distracting amount of options available and be able to focus on what online options really matter.