.zip vs .tar.gz

[J. Todd Slack]

Hi All,

I have a bunch of old data that I want to compress up but still keep  
on my system.

So .zip vs .tar.gz?

Which will produce a smaller archive?

I know that I can pass a -9 to .gzip for max compression. Some of  
these folders are gigs a piece...Testing this would take a long time  
for me given the sizes of some items.

Does anybody have thoughts?

Is there a finder contextual menu extension where I can say  
"Compress .tar.gz" just like there is to .compress .zip?

Thanks,
-Jason