I prefer backup and restore where I can do it (primary limitation would be disk space) because you don't ever risk the fundamental data files. Detach and attach, you take a risk that during one of the three operations, detaching, copying, attaching, something could go south and that's your database. In short, you'd need a backup in place as a paranoia point anyway.

Plus, with backups, you can combine a log shipping process with backups to arrive at a place where you have very minimal down time. Just the time to disconnect the users, do a final backup of the log, restore it, and bring the users back online.

Safe, fast, and flexible with backups, not so much with detach/attach.