There is no upgrade path from 2.2 to 3. You have to do a fresh install. Either method you listed will work. The time it takes to create a template from a VM in 2.2 is tremendously long, so I found it easier to tar-gzip the shutdown guest and save it off on another server and then import that into 3.1.
Sorry to resurrect an old thread, but I have to say that the SimpleHTTPServer method with multiple file entries is SO much faster than the tar and gzip method that I had been previously using. It is definitely THE way to move VMs from 2.2 to 3.1.
Yes, I agree, we've done whole machine moves using the template import method (of course with the python http server) and we've also done single disk imports, and creating a new VM and attaching those disks.
We've witnessed in moving some VMs verbatim, sometimes the vnc password in vm.cfg gets retained and you have to manually edit the vm.cfg on OVM 3.1 to remove it otherwise the console will not function.