The primary question is probably one of coverage. Many technologies are limited in the areas they cover. The next question is speed or bandwidth. Higher speed means that more data can be delivered. In practice this means that with high speed we may deliver multimedia content or pictures.
Medium speed is good for large amounts of text and small pictures.
Slow speed or low bandwidth is good for short text messages. Another important consideration is latency, or how long it takes to deliver a message. Paging systems can have delays of 30 seconds to several minutes. Some latency may be introduced by the underlying technology. Web pages or wml sites may introduce delays when they are under heavy usage.