In my (totally biased opinion - lol) the benefits of the Basal-IQ algorithm on the Tandem t:slim X2 (which require the G6 integrated in order to function) totally trump any other discussions about which cgm is better or preferred for any reason.
As long as the G6 is accurate enough ON YOU to properly drive the Basal-IQ algorithm on the X2, then the combination is a complete game changer.
At this point it seems fairly clear that technical behavior of the G6 can be substantially different enough from person to person that it may work perfectly fine for one person while operating absolutely horribly for a different person.
With the Control-IQ algorithm forecast for launch this Summer of 2019, we (personally) will have to see what the feedback is on Control-IQ. As of right now, I am super happy with Basal-IQ.