The move to a quarterly release pace has been announced recently, and 17.2 is the first version adhering to that scheme.
It came straight after 4.2, and the very page you mentioned has links to the release notes.and list of included fixes.
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And 17.2 would have probably been a version 4.2.1 - an update to version 4.2.0 with lots and lots of bug fixes. So I'd say there's little reason to choose 4.2.0 over 17.2.0 - and there are a few feature tweaks and improvements as well.
17.3 will drop not too far from now. Which means more bug fixes on the way.