I am (was) an Garmin only guy. Of late I am not impressed with Garmin durability or customer support. I have a close friend who's boat I run from time to time and the Garmin (less than 2 years old) has not stood up like old units. The interface and UI has progressed backwards in my opinion and there has been some
comparability compatibility issues. Customer support has been average at best.
Compare this to Lowrance. My Scout had an old (6 plus years old) unit. I had an electrical problem on the boat which spiked power to all my electronics.

The unit was DOA. I sent it to Lowrance and they tested it. They offered a new unit at a discounted price. Something that Garmin didn't offer to replace the unit which had a poorly designed water seal on the screen. I installed the new HDS7 Gen II on my Scout only to find the fuel sending unit which plugs into the GPS was also toast. I contacted Lorance to purchase a replacement and they send a new one gratis.
The UI on the HDS is superior IMHO to the Garmin. The screen is clearer and better handles glare. Mapping detail is generally good but does lack some detail compared to Garmin in the areas I fish. However not to the point that I would consider changing it. Sonar capabilities and detail far exceed what I've experienced with the Garmin.
I'm a stubborn SOB. I will stick with a company for a long time because I don't like change. Well, I've changed my mind. In no small part due to what I feel is a superior over all product.
I highly suggest that you go to your local marine supplier. Look at each unit side by side. Then make the right decision based on your needs.
Cheers