Hyper-V backup of guests - truncating the log

Hello

I've found a few documents about the backing up of Hyper-V guests but can anyone confirm:

Windows server 2008 running 2 VMs:

Exchange 2010
SQL 2008

What is the best practice for backup?

Run internal backups on the guest VMs, then backup the VMs from the host (windows backup/diskshadow)

I'd rather not install an agent on the guest.

Thanks

John

Me