I have used an Wahoo Elemnt for many years and recently switch to a Garmin 830 because I really wanted the Radar support and Wahoo at the time had no mention of ever supporting it (that is no longer the case). However now that I have switched I like the 830 much better for a few specific reasons that most reviews do not get into.
1. Di2 support, it is much much better on the 830.
It does a better job letting you know the battery level, allows you to assign the battery level to a field if you want.
It gives you an interface to show you want MODE your Di2 is in and allows you to change it, wahoo does neither of these.
And most important is if you have Di2 in synchronous mode the 830 will make a chime and pop a notification warning you that the NEXT shift will be a big ring shift. This make using Di2 sync mode possible in my opinion, until I had this I did not like the sync mode because I did not like the surprise big ring shifts.
Also unlike the Wahoo, Garmin lets you define what the top buttons on the Di2 do, including support for short-press, double-tap, long press.
2. I already had the Garmin Vector pedals and naturally the 830 had better support for them, more importantly it would calibrate them reliably. The wahoo it was always a hit or miss on calibration.
3. Third party fields and apps. At first I did not think much of this but they really can be nice. I personally really like the Wind Field, it requires your phone for data but it shows you semi-realtime wind and direction so you can look down and see yes in fact I am going into a headwind.
Really the only downside to the Garmin over the Wahoo, is getting your initial data fields setup is harder since on the Wahoo you can do that on your phone. However you really only do that step once. If you want to fine tune it I think the Garmin is better since you can do that right on the device while on the ride. With the Wahoo I always had to make a mental note as to what I wanted changed and change it later.