I haven't had experience with some of the brands mentioned here, but I have owned several Garmins, 2 TomToms and a flash 1din dash unit with a 7" slide out/pop-up touch screen display.
I spoke Garmin for many years and owned a Camper 770 until last November. I love the Garmins in all respects except 1. They are utter failures at managing map updates .
I've lived the van life for 9 years, during which I have only had access to Mobile Broadband which is always metered, I have a monthly ration.
To get the Garmin device to connect to the internet, I HAVE to have a MS Windows machine to act as an intermediary. I have mostly experienced failed updates that restart from GO instead of resumming a broken download. This poor quality map update service has frequently used up my entire months rations of 3G with nothing to show for it.
But the key issue for me is that I have to have a Windoze machine to update the Garmins. I am a MicroSoft hater and will never use any of their products unless I am forced to (eg Garmin updates). I get over this by re-configuring all of my computers to dual-boot, which allows me to select either Windows or Linux Mint (or any other distro that you may admire).
So after wasting several days and all of my 4G mobile data allowance, while sitting under some trees in Adinkerke, I bought a TomTom and began to learn it's language.
Thankfully the TomTom is as intuitive as the Garmins are. I easily found my way around the menus.
Massive plus for the TomToms is that I don't need a Windows Laptop/PC to update the maps etc.
In fact I don't need a computer at all, the TomTom has WiFi built right into the device.
Some of the TomTom are also available with a SIM card that updates itself when needed. These ones don't even use your data rations, they do their own thing in the background.
I've got the TomTom GO Camper right now which offers 3 connection options for updates, USB tethering to a laptop/pc, wifi or bluetooth.
I've found that if I use the Android phone's wifi hotspot as the TomTom gateway to the internet, it chugs away and tells me when it has completed.
Overall, the TomTom updates have all been stress and problem free
Garmin will winge at you that it has failed, offer you little to zero help as to how/why it failed. This leaves you no other option but to repeat previous steps in the hope that it will work, this time will be different....
With regard to the Xtron pop up in dash unit, waste of money. The unit I had was rubbish, it was trying to be too many things, radio, cd player, mp3 player, in-car navigation.
I was unable to track down any map updates for it, so it rapidly became useless for navigation. The build quality is typical cheap and nasty eastern origin garbage.
I've become fairly fluent in TomTom quite easily and I became a big TomTom fan very quickly. I am now free from the need for a windows laptop simply to update Garmin maps. That fact alone is a major plus for me.