I'd also recommend the Liestal Chienbäse on the 21st evening.
http://www.chienbaese-verein.ch/chie...aeseumzug.html
I've been twice before, and it's really pretty amazing. Here's some photos from when I was there the last time:
http://roshan.info/gallery/view/plac...e08/?g2_page=4
We went to Liestal for the Chienbäse in the evening, went to Basel almost immediately after and hung around in Basel till the Fasnacht parades started. I'll probably be doing the same again this year, planning to head to Liestal to be there by 18:00.