Not sure where to start? In the past this was often dictated by access to the technology and the resources to create the ads. Since AdCritter solved both those issues, it comes down to what's best for your business. Which one's right for you?
TV: Good for targeting. Very good for credibility building. Because they are both interruptive and unskippable, TV commercials are outstanding for ensuring the viewer actually sees and retains your message. As such, they are the most expensive per view.
Internet: Great for precision targeting. Also really good for testing new messaging. (For example, running three different headlines to quickly see what gets the most clicks). It is not particularly good for credibility building, as many low-quality and even scammy businesses advertise online.
Billboards: Can only be targeted by location. Very good for credibility building. Ideal for raising brand awareness across a particular city or metro. Not well suited for businesses with very narrow target audiences.