I am aware of only three available CGMs in the US today: The Dexcom G4, the Dexcom G5, and the Medtronic Enlite. There used to be one more, the Abbott Navigator, but it was withdrawn from the US market about 4 years ago.
The Medtronic Enlite had a very rough start, with many complaints and worries about accuracy, but seems to have stabilized. The Dexcom G4 and G5 are strong and mature systems.
The Enlite requires 3-4 calibrations per day. It can be a bit picky about how to redo a missed calibration. There are no communities of users that I know of where you can find great calibration recipes for the Enlite.
The Dexcom G4 and G5 require 2-3 calibrations per day. Users have come up with fairly sophisticated routines to optimize them and ensure that the actual reading is close to reality -- a good forum to discuss that may be https://forum.FUDiabetes.org . I can provide no proof for that, but I consider that almost all the calibration recipes you get there for the G4 and G5 would work for the Enlite as well - very little is specific to the Dexcom CGMs.
The Freestyle Libre Pro is not a consumer CGM. Its function is really different: your doctor gives you the sensor, you wear it for 2 weeks without knowing what it measures, then your doctor downloads the results. It is a diagnostic tool, not a diabetes management tool.
However, there is another Freestyle available that you may be aware of, the Freestyle Libre. The Freestyle Libre is actually a pretty cool idea, although not quite a consumer CGM either. Essentially, it is a sensor without a transmitter -- and, like the Freestyle Libre Pro, it dos not need calibration either! You need to manually pass a reader over it to read the result. So you can get a result anytime you want, but you do not get a track that you can view like you do with a Dexcom. The difference may seem small but is actually a giant one when trying to manage blood glucose. Nonetheless, the Freestyle Libre, with its much lower cost, is a great tool that fulfills a different need.
Unfortunately, the Freestyle Libre is not available in the US yet.
So, in the end -- there is no CGM that I know of which is present in the US but does not require calibration. If I had to pick:
- if I had good insurance I would pick a G5
- if I did not have good insurance I would pick a G4 (it is possible to pay a lot less for transmitters per year with the G4 -- but that is another story).