Your "which version" question depends on your tolerance for risk. The 1.4.3 version runs on Joomla! 1.5.x in Legacy mode. It is old and stable despite it's "RC" tag.
The new 1.5.x series of JEvents will run on Joomla! 1.5.x in native mode. The version that you installed is an "old" beta ("old" being a month or so in this context). You will be much happier if you look in the JEvents 1.5 Release Candidate forum and pull the latest release from this link
. As of this minute that is 1417. This is SVN code, development code. That makes some folks nervous, but that version has all the sexy new features in it. It is very close to a stable release. Especially for evaluation purposes, that is the version you should look at. That way you get to play with the new toys without putting SVN code on a production site.