In the past, I've never had a firm preference for either of these sites - they both have their good and bad points. A recent update from Wikispaces shows the route that this site is headed in, monetization through additional features - the Freemium model. The latest paid feature to be added to Wikispaces is custom permissions, giving paid users more control over who can view and edit their ePortfolio.
The bad news from our perspective is that this feature costs $200 a year. To me, this amount is a bit steep, and it's certainly not something that our students would be likely to pay, so for now, we're stuck with public/private as their ePortfolio access status.