I migrated to Unfuddle. I like it, speed seems to me better than what I had at Assembla. But, Assembla had better options:
Assembla had a web-based interface for exporting/backuping (svnadmin dump) and importing a repository. It helps migrations and it allows me to backup once in a while the repository. With Unfuddle you have to request the staff to do it for you. For large repositories you have to find a way to send them your dump file for importation. Not exactly simple.
Accounts were "global" at Assembla. Meaning that with a single account I could work on many other projects hosted under different accounts. Accounts are "local" at Unfuddle. Each project has its own list of users and credentials.
I looked at OpenSvn but the website and BIG WARNING sign are not inspiring. I tried to open an account but never received the confirmation email, so no luck there.
I think DevjaVu could be a nice alternative, but I could not open an account. It is under invitation only, so no luck there either.
I have a friend of mine which migrated from Assembla to Origo. He likes it. We checked their web interface and they have the web-based svnadmin dump available, but no web-based import. I can't say about the accounts "scope". Still, it is a student initiative, will it last? How safe is the data?