For software engineering sprints, it is better to start sprints in the middle of the week as opposed to Mondays. This is counter-intuitive as the natural cadence for business is Monday through Friday, so why is software engineering different?
Individual software engineers need to estimate the amount of work they can get done in a sprint, and sometimes they are wrong. This means they either need to put in more work to hit their sprint deadline, or they need to have a conversation with stakeholders about the work slipping.
If you are going to put in more work, it is socially easier to do that on a weekday. If you need to discuss a sprint task with stakeholders, you might be able to reuse an existing Monday meeting for that purpose (but not always).
All else being equal, it is better to have happier coworkers, so start your sprint mid-week. I’ve used Tuesday and Wednesday in the past and most teams naturally seem to prefer Wednesday.