I advise new teams to start with 1 week sprints, because:
- You from new habits quicker when you have the ceremonies every week.
- You learn to deliver smaller batches when you MUST get some thing done within a week.
- The ceremonies are shorter and feel less invasive.
- You'll do more experimentation with the process.
- You get faster learning cycles.
There is another reason that may be more compelling, depending on the reasons for choosing Scrum in the first place: Team effectiveness.
Retrospectives are the Scrum ceremony where process changes are discussed. I call them "experiments", because the team is changing something they hope will work out - not something they have experience with.
If you do 1 significant process experiment per Sprint, denoting that Significant means a 5% difference in results (although this is hard to quantify), assuming half of your experiments succeed, within 1 year:
- If you do 1 Retrospective every 4 weeks, you will be about 35% better. That will hardly be visible.
- If you do weekly Retros, it will be about 200% better. That is a massive leap which everyone inside and around the team will notice.
Where do you want to be after your first year?