I prefer Chrome because its updater also includes the flash plugin, and it has its own pdf-reader plugin.
Chromium also doesn't do releases, just lots of bleeding edge snapshots, and one or two of those have been badly broken.
I switched from Chromium for the PDF reader. It's nice.
For a while, just copying the PDF reader plugin from a Chrome installation to a Chromium installation worked for me. I've switched to FF Nightly, but you could give it a try to see if it works.