According to Wikipedia:
"The Baez recording had some changes in the lyrics. Baez later told Rolling Stone's Kurt Loder that she initially learned the song by listening to the recording on the Band's album, and had never seen the printed lyrics at the time she recorded it, and thus sang the lyrics as she had (mis)heard them. In more recent years in her concerts, Baez has performed the song as originally written by Robertson."

Many people prefer the Baez version (it made several Top 100 lists and became a gold record), which may in part be due to Joan's voice being more pleasing. Levon Helm's version, while authentic (as a co-writer with Robertson) suffers by comparison.

Sorry, KimC and others, don't mean to disrespect The Band.