I'm a communications contractor, installing computer/telephone cabling and locally handling national equipment rollouts, so I'm frequently going to places I've never been before. My first experience with GPS navigation was 5 years ago, using Telenav on my Nextel handset. I later switched to VIAMOTO (I could get it for free, and liked it better). I thought it was the greatest thing since sliced bread. After a little over a year I decided to go for a standalone unit because phone calls would routinely interrupt navigation. I chose a Garmin StreetPilot c550 with TMC traffic because I recognized the name, thought traffic would be a great thing to have, and I didn't feel like doing a lot of research.
After a short honeymoon, I realized that the simplistic interface was far too limiting, TMC traffic didn't work worth a *%^*, and the guidance it provided (the instructions to keep you on the chosen route) were often poor - too many keep left/right when not needed, and not enough when they were needed. Thus I began my search for something better, particularly with regard to guidance, often switching back to VIAMOTO on my Nextel handset. That's when I discovered the TomTom Go 920.
Guidance on the TomTom seemed obviously superior to the Garmin, the detour function was actually usable, I could avoid roads (for commercial vehicles), and I loved the idea of PLUS traffic over GPRS - no more problems with non-existent FM reception for traffic. The data connection through the phone was easy to setup, and PLUS traffic seemed a lot more accurate and reliable than what Garmin offered. For a month or two I drove with both the Garmin and TomTom on my windshield, feeling better about my decision every day due to the TomTom outperforming the Garmin.
Within a year I dropped my Nextel service and switched to Verizon, who wanted $30/month so I could tether my TomTom to my Blackberry. For a while I kept the Nextel phone using a Boost Mobile SIM card for use only with PLUS traffic. But when the Go 740 LIVE became available, I opted to go with that, as the monthly costs ended up being cheaper.
Despite my frustrations with TomTom, I doubt I would ever go back to a Garmin, since the deal breaker was their guidance, which was working as intended, so there was no hope of it ever changing to my liking.