There are two or three basic approachs to tracking collars.
1. GPS based using cell phone towers
GPS is really the only one to consider. Bluetooth depends on being within bluetooth ranges of your pet or having a bunch of people download an app to crowdsource your dog. Pretty useless out in the boonies where we are -- or in a city where buildings block bluetooth range.
Here are my top five:
My NEW favorite! This is another new entry into this niche and it's sounding really really attractive, especially for those of you who have wanderers, like Great Pyrs or Beagles or Coonies. It's a true GPS system built into its own collar. The insantly attractive feature of it is that it's got up to a 2-3 MONTH battery life! I've known a number of dogs who couldn't be trapped before their tracker battery expired, so this would be a huge advantage.
Formerly called Tagg, this was the first system we used and the one we currently have on three dogs. I do like it. Pro: dependable, and now that they've fixed the collar attachment, pretty reliable about staying on. Good coverage all over our area: Con: the former version would show you old tracks inside your area so you could figure out where the dog was getting out. Plus there are some requirements on the router at your house in order for Whistle to work with it. My neighbors weren't able to get their Whistle's working with their super dooper new property-wide router. But pretty much a good, dependable system and one we use now.
This is my next system, I think. I like it because it's true GPS AND it will show tracks inside the boundary area so you can figure out where that danged weak spot in the fence is!