In nature, evolution occurs most rapidly when competition for resources is intense. The same process is now occurring with promotional media. All traditional media channels are now saturated, and competition for consumer attention is intense. At the same time, the impact of any one medium is becoming diluted. There are many more TV and radio channels, consumer have the ability to skip adverts and free information is now much more accessible. As a result, companies are becoming increasingly innovative in their approach to communications and a host of new media channels have emerged. As a result, media choice is becoming a tricky task, which is why detailed segmentation is so important - it's no use starting a Twitter campaign if none of your target market are regular users of the site.
Highly targeted communications often lead to better results. You can usually expect a response rate of under 1% for a relatively generic mass mailing. However, personal letters to a handful of your most loyal customers would lead to a dramatically increased rate of return. When deciding which media to use consider the reach, frequency, media impact and what you can expect for your budget but most of all, ensure your target customer will see the message in the first place.
Media choice is a matter of compromise between volume of people versus the personalisation of the message.