YRV - Since it is more mpv like, it has a little more space and
headroom. I don't know about the seat configuration, but the very
least it should be able to fold out for more storage space. Yes,
the engine is from toyota and although the engine make a major
component of the car, it is not the only component. I guess it is
whether the synergy of all the parts that give you the
satisfaction. I agree that it is unique, but quite subjective. In
comparision on unique-lity, i would rather go for March or the
Ignis 1.3
Vios - Very nice car and it is really powerful (in 1.5 catagory
terms), mainly due to its vvti engine + 970kg weight and fuel
consumption is good. Cruising is also comfortable. However, being a
sedan here, it can only offer you what a sedan can offer
space-wise. I do totally agree with you too that it is very
common.
March - March is marketed as a car with "so March (much) more
intelligent" and "so March feature". As the name implies, it is
"intelligent". Features features that can only be found in
expensive cars, e.g a keyless entry keyless start, digital display,
speed sensitive wiper. As for space wise, I am not sure it is
offers as much as space as car of its class.
Maybe you would like to test drive all of them first to find out
how they perform on the road before making a decision. 
