I am from Australia and I have been using GPS Sat Nav for years. I have own quite a few, but let me tell you that my best experience is with Mitac Mio.
For those of you who do not know this brand, they are one of the pioneers in manufacturing satellite mobile phones, satellite tracking device, and most recently, mass producing GPS Sat Nav.
They are one of the most accurate and quickest Sat Nav you can buy in the market today, not only that, they also have the most user friendly mapping browser plus user interface of all other brands in the market.
The next brand I would recommend is Navman. They are tough and reliable, have good reputation, but they have poor map design and interface. Route re-calculation is slower than Mio, however locking to satellite is extremely fast even under thick grey clouds in the sky.
Garmin is one of the most reputable brands in Asia due to its mapping popularity. It hasn't come alone nicely, older models were big fat and chunky. Poor satellite locking especially on cold start (they take forever to lock in), route re-calculation is slow, very important when you missed a turn, you want the device to provide the next best alternate route.
Tom Tom is by far the worst performer in this market, it has the largest screen you can buy for a Sat Nav however it is far worse than Garmin.
The only this Mitac Mio is lacking is its ability to purchase maps for other country and use it in the same device. For example, Mio Sat Nav unit you purchase in Australia will only work with Australian maps, if you purchase maps for another country and saved in it the SD Card, it will not work on the Australia unit.
However when comparing everything else, it is the most accurate GPS, partly due to its fast processing time which means, it will ask you to turn before you need to turn, which gives you plenty of time to prepare to turn. Where as the other units would turn you to turn at exactly the time you should turn. Most of the time, you would already have missed your turn by the time the voice guides speak.