The copyDB wizard is not perfect: for my taste too many things to consider (e.g. internal IDs) for it to work.

I used backup/restore switching the level afterwards if possible depending on the application. Some packaged software use still 80 (SQL2000).

detach/attach works too, but since I had to switch hardware completely too merging different servers into one big I found backups having the smallest number of files the easiest to handle - for that simpel reason I've chosen backups. I guess it does not really matter.