I do all my shopping the first Saturday in December. I find this date to be a happy medium for me - I can still find a parking space and the crowds are busy, but not insane because everyone still has a few more weeks of shopping available.
The days before and Christmas Eve I avoid shopping all together. I've never shopped that close to Christmas and while some people may enjoy the last minute rush, I have a feeling it would ruin the experience for me. I like the crowds, but last minute shoppers can be unfortunately aggressive from what I've heard...So I stick to a few weeks before!