I’ve used both Garmin and Wahoo Bolt extensively. There are some definite pro’s and con’s with both.
The Bolt is small, aero, and extremely user friendly to set up. Everything is so easy to set up from your smartphone. It also integrates beautifully with RideWithGPS. I’d go to RidewithGPS website, create a route using their very good tools, and then be instantly able to sync the ride over to my Wahoo via my smartphone. Battery life is great, screen is easy to read. But the downside is that it doesn’t integrate with a few things well. I became a big fan of the Garmin Varia rear radar this year after Nate mentioned it on a podcast. I ride a lot of quiet country roads and the Varia has made me feel so much more confident knowing when vehicle were approaching. Initially I used the Varia head unit, so had the Bolt and the Varia head unit mounted, but ultimately went back to Garmin so that it was all on one unit. The other aspect of the Bolt that was not as good as the Garmin was the DI2 integration. I like using the buttons on my shifters to change the display page, something that works well on Garmin. I also have the gear ratios/shift mode displayed on one of my screen when using Garmin, but I don’t think the Bolt offers this.
With Garmin you have a wide product line range of head units, so you can pick based on budget and features. It’s more of a pain to get your routes onto the Garmin with the default requiring you to directly connect the Garmin to your compute and sync with Garmin Express. There are workarounds though, and I used dynamic.watch. Their app on the Garmin let’s me pull in routes that I’ve created (or imported form RidewithGPS) and loaded on the dynamic.watch website directly onto my 1030. I also recently started playing with the “light network” feature on Garmin after I started using a small Bontrager Ion 200 RT daytime light. I’ve found it a little bit buggy and the light network seems to spontaneously disconnect and connect during rides, but the light keeps working.
Some of the Garmin units offer the “Firstbeat” fitness metrics. They aren’t ground breaking but it is somewhat interesting to see after a ride how much aerobic and anaerobic benefit it supposedly provided.
One other thought is whether something like a Garmin Fenix 5 Plus my serve you well. The display is smaller than most head units, but the Fenix’s provide most of the same features that a Garmin head unit provides, plus its a great multisport device, sleep tracker, etc. They were pretty expensive when launched, but I’ve seen a few sites have the new Plus series on for 15% recently.