We typically do sprint demos on Thursday afternoons, disuse the sprint progress with stakeholders on Friday, officially end the sprint that day and then start sprint planning on Monday. There can be problems with people being off for long weekends or holidays, but in general that's not been too much of a problem, and by doing the demos on Thursday afternoons that helps a bit. We realize that the demos might not have all the features in place, but we try and reserve Fridays for lower priority bug fixes or loose ends to tie up to finish off the sprint. A weekend break is also nice as a Scrum Master or Product Owner/Manager, because you can use the weekend to react to stakeholder priorities as needed.
Most importantly, what do the teams think? Let them have a significant say in when your sprints start and end.
Other teams have found that starting in the middle works better for them. These links pose that a mid-week start can be helpful:
What's your best practice?
