First, decide on what dimensions you want.
one of the mini 3.5" screens, or a bit larger at 5", or like me the 7" screens.
The larger screesn typically have a bit better speaker for better sounding audio output.
If you are new to the market, drop in at a retailer where they have a few of them on display and get your fingers wet fiddling with the different ones.
I'm fond of the Garmin brands myself. I have used a Tom Tom almost 20 years ago, and had a Magellan at one point, also many years ago. I left them because Garmin, IMO, had a better menu system and "seemed to" have a better database.... but that again, is a 20 year old experience.
What features are you looking for?
- Audio output jacks are nearly a requirement.
- Bluetooth is quite popular, but I don't use it, found it to be conflicting with other devices, like my cellphone..... I found that having the GPS trying to answer the phone was big PITA.
- Menu structure is important
- how easy is the search function for you
- Look ahead is a Garmin feature that I can't do without, this shows you the next gas, $$ ATM, Food, Rest Areas that are upcoming and how far away.
- Look at the mounting methods
- How long will it work without a power source?
- Do you intend to carry it with you when on a hike?
- Is the screen legible to you?
- How much do you want to pay?
those are things that I consider.
for sources, hit the internet... I like to use www.SearchTemptest.com
to find things in the used and new markets all at once.
is a major dealer and have great adverts explaining what each model can do.