I have only used Garmin, currently have an edge 820, so I am biased. Nonetheless, it has been great and works well with many add ons in the future that you may not have yet.
Having speed, cadence, etc.is good but you are likely going to want a power meter at some point. Monitoring your power output is, IMO, a better way to monitor your improvement. If you a month ago, you averaged 180 watts on a ride but can now do it in 200, you are getting stronger. Your speed average can vary greatly based on terrain and/or weather/wind. On windy days or hilly rides, I average a slower pace. However, I know I'm doing well if I'm maintaining the same or improving my power output.
The other feature I love on my Garmin is the radar (add on device) that notifies me of vehicles approaching and their distance. I know I can't control approaching drivers but having an increase situational awareness helps keep me safer.
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