My company is currently using HAProxy 2.0.13 (from Ubuntu repository).
Since latest HAProxy (just released last month) is 2.5, we think HAProxy 2.0.13 is a bit “long in the tooth”. Also, (claimed) performance improvements of 2.1 seems to be a ‘nice to have’.
But for production you should use 2.4, because 2.4 is a LTS release and will be supported for years to come, while 2.5 is not. Also using a .0 release is probably not a good idea anyway.