Avid's are:
- inexpensive
- simple
- easy tool free adjustment
- easy tool free pad replacement
- field repairable
- fade free braking on long steep descents
- excellent performance in wet or snowy conditions
- don't wear out your rims
- don't overheat your rims
The downsides are:
- higher weight than other brakes
- require more wheel dish than other brakes
- can only use disc wheels
For my money the Avids win hands down if you want trouble free braking in all weather conditions and in steep terrain - like a brevet for example.
I can't imagine buying another bike that doesn't sport a pair of these fine stoppers.