I can't tell you that for certain which sashiko needle is best to use. It depends on a few variables.
I've listed some of these, and my thoughts about the needles we carry online, in this blog entry.
Sashiko needles are longer and thicker than the needles most of us use, and most have large eyes for threading thick cotton sashiko threads.
Olympus Sashiko Threads
This entry is just eye candy - too much color to not share!