In principle they are the same, the OVA is just another way of packaging the files.
From the VMware documentation "OVF is a file format that supports exchange of virtual appliances across products and platforms. OVA is a single file distribution of the same file package."
A single file OVA is a tar package of the OVF files.
I personally find a single OVA file easier to distribute and store.
A potential drawback could be the extra extraction step you need with an OVA file.
Thanks for your reply,
I was hoping that because the OVA format is a tar file that it would compress the data a bit. But I have found that using the defaults in ovftool the file size doesn't change any significant amount between the collection of files for ovf and the final ova file.
Either way it is much easier to deal with single ova files within the format of my PowerCLI script, so I will go with that.
One method that seems to reduce the size of an OVA file is to zero out the free space on the VMDK(s).
I'm not sure what the side effects might be, so, test and use at your own risk.