Choosing the right flash unit for a job depends on a host of factors. There is no one perfect flash unit for all purposes.
Before shopping for a flash unit, consider how it’s likely to be used. Is it needed just for occasional snapshots? For heavy use out in the field? For indoor amateur studio work? What about size and weight? After all, a high-end flash unit is bigger than a consumer camera. What budget restrictions are there? Are there any plans to expand to a wireless system, or is a single on-camera flash unit adequate?
Here are a few suggestions for various types of flash usage.
A flash unit for casual and occasional use with a Canon digital camera