Vitz is definitely better in build quality than a PAK civic.
BUT
Its suspension isn't as soft as a Corolla on potholes. It has awesome road grip, which means not TOO SOFT suspension.
nathia gali 1.0 will be "OK", not excellent, will take you up in S but on a full car a bit sluggishly. Of course, 1.3 is much better and super fun and thrill to drive.. can take you anywhere in a thrilling way...
Ground clearance is also an issue in Vitz as it is not raised like a truck.
So, for potholes + soft suspension + mountain driving.. get Grande or 1.6 Altis. GLI doesn't have good enough power.