I would actually opt for the Vios than the Mirage for the following reasons:
Visually, the Mirage appears to be smaller and appears to have a shorter wheelbase even though both are subcompact. As such, I feel road stability is better in the Vios. Since you plan on using it in the highways, I would prefer a slightly bigger/stable car. You will notice that at speed, if larger vehicles pass you (esp trucks and buses), they tend to push greater quantities of air to the side, and that can actually shake your vehicle (at speed). Given the dynamics of the Mirage, I would say it would have skinny tires as well to help with reducing road friction hence helping fuel economy. With less rubber on the ground, you theoretically have lesser grip to a certain extent. And as such, you might find this unnerving when you drive along the expressways and these road behemoths pass you. This is a valid concern I believe as I experienced this in an Innova 2004 model when I drove it around 100kph (this was due already to aerodynamics of the vehicle not delivering enough downforce I think). The steering felt loose at speed and gusts from the side rocked the car. I just had to slow down to 80kph as I was unable to keep it straight and steady (same experience when our driver drove it - he did the same)
The Vios is tried and tested in our shores. Granted, I also like the Mirage, but I tend to avoid being one of the first people to buy something as it is theoretically not yet publicly tested (although possibly field tested). An example I could give is the old D4D problem, the Hyundai Getz 1.4 engine knocks because of fuel, Fiesta AT transmission slipping on 1st and 2nd gear (comp seems having difficulty choosing which one to hold on to), old 2001 Pajero aircon problem (design problem that had the underside actually end up collecting water which made the cabin air stink when using the AC) and so on and so forth. So I choose peace of mind as I won't be the only one driving it or rather, I won't be driving it.
I am not trying to scare you away from the Mirage, although I am just giving out my own experiences and a few friends on the matter as you are basically choosing a new model to be launched in our shores and a long standing one used by many.
I don't think you would have problems in servicing of either of the vehicles, at least that I can believe wholeheartedly.
Cheers and good luck in your purchase.