gzip vs bzip2

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.