It is best to use the OVF import as it would contain a lot of settings that the distributor of the VM appliance (in this case Microsoft) that they see it as minimum requirements. The vmdk also grown in size from 21.9GB to over 40GB so it looks like the vmdk was also compressed and the import via OVF also decompressed it.
For UEFI vs BIOS, you can see that the virtual disk has MBR (from diskmgmt.msc inside the Windows 10 VM). So that means it would work with BIOS and not with UEFI as UEFI would require a GPT. As you can see changing the Firmware type shows a warning that it can make the VM unbootable.
If you would like to use UEFI (for whatever reason) you can use the MBR2GPT tool to convert. But given that the VM expires every 30 days, you would have to be doing this for every import of this Microsoft developer VM unless in the future Microsoft distributes the VM pre-configured with UEFI instead of BIOS for firmware type.
