i've lost track of how many vm images i've moved back and forth.
trying to find the fastest way, i've done some comparisons of compression options available.
benchmark was run against a 10GB vmdk containing only a clean windows install.
Packer Minutes Compressed Size Percentage
bzip2 -1 35 5882676084 56.1%
bzip2 -9 41 5805348305 55.3%
gzip -1 13 5993116500 57.1%
gzip -9 20 5834635837 55.6%
while bzip2 is the clear winner over size, its running time limits its usage where time is not an issue.
most of the times gzip -1 is the best choice.