However you choose what to play the important point is that you are playing. That being said I'll offer some thoughts.
Randomly selecting scenarios is fine if your objective is just to have fun, and that is an excellent objective.
If your objective is to learn something specific, such as Night, Caves, DTO or whatever, repeated playings of that genre is the way to go. IMO there is no problem learning by repetition.
If you want to do a Series Replay or AAR play the scenario several times in a row before sitting down to do the version that will be presented to the public. Your final product should be better than if you just winged it. We played Guryev's Headquarters at least seven times before doing the Replay.
Playtesting. Depends what the designer wants. Are there many scenarios he wants played and what is the time frame for completing the project? Important work though.
Enough thoughts for now. Enjoy whatever you choose to play.