Sorry, I haven’t been feeling well, and I haven’t taken the time to really look into this particular thread.
The Big Metal Box Issue
I will say, cars are always challenging because you’re talking about a big metal box, often with tinted glass, both of which degrade signal significantly. So getting signal out of the car to begin with can be complicated, particularly for low energy devices. It’s not impossible obviously, but it does add additional challenges.
Also, typically signal will travel very differently through an empty garage and one that has a car in it. Again, big metal box. this is one reason why people get a lot of erratic results, especially if they have two cars that go in the garage as now there are many different possibilities: no cars, car on the left but not the right, car on the right but not the left, one car coming in as another is going out, etc.
And of course local architecture variations. Garage doors, in particular, can have really different architecture as far as blocking signal. One with clear glass window inserts all the way across will typically have a much easier time than one which is either solid or which has tinted glass.
And of course different garage doors are made of different materials. Plain wood is a lot easier to get signal through than something with a fiberglass core. Or again a metal door.
For all of these reasons, I like to put a repeater near a clear glass window on the same side of the house as the garage. It can just make life a whole lot easier.
And again, all of this helps explain why different people report different experiences with the various different presence methods. 
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Detection zone
There’s also the question of how big you want the detection zone to be, which varies from household to household.
If you want the garage door to be open before you get to the end of the driveway, you almost have to use phone based GPS Geofencing or Wi-Fi detection. Even though the SmartThings zigbee presence sensor as a range of around 15 m, it only checks in every 30 seconds. So you could easily have a 45 seconds to one minute delay before the garage door starts opening.
If you’re the sort of person who’s OK waiting in your driveway for the garage door to open, no problem. But if you’re the sort of person who wants the door open already as you pull in the driveway, the presence sensor probably won’t work for you. This is a personality difference, not a technical one, which again is why some people will be happy and some will be unhappy with the same technology.
My personal requirements are a need for hands-free operation, but I don’t mind Waiting a little bit. Which is why I personally use ibeacon detection. It’s very precise, and it is a little faster than the 30 second presence sensor, but, yes, I am sitting and waiting for the door to open each time. Which won’t satisfy everyone.
So before we start brainstorming specifics, if you could give us a little more of an idea of what you want the experience to be. You’re driving up in your car, at what point do you want the garage door to be all the way open? Before you reach the driveway, or after you’ve pulled into the driveway, but you’re OK with waiting a minute or two? This will significantly affect the possible solutions.