each is somewhat different, and a compromise one way or the other. so it depends upon your priorities.
a few aspects include:
*147GTA: smallest/least bootspace; shorter wheelbase = more 'chuckable' handling; least rear legroom; 3-door = more difficult rearseat access for children/passengers; VDC; not all have leather
*156GTA: decent boot; decent rear legroom; 4-door, so easy rearseat access; no VDC which might be a safety consideration for a 'family'
*V6 GT: hatcback = practical bootspace; same wheelbase/legroom as 156; 3-door = more difficult rearseat access; VDC; lots of mod-cons (subject to country/market and options) incl rear parking sensors, etc; meant to have the most 'comfortable' suspension/ride quality
so, whilst the 156GTA is probably the most practical for a young family, the lack of VDC is a significant blight in my books (comparatively). though of course, the grip is excellent, and you just have to drive safely!
all share a similar growly, throaty engine/intake/exhaust.
mileage is only part of the equation for a quality car. you obviously have to also consider if it's been in any accidents, or has been driven 'hard'; these can be hard to determine. i think a FSH is essential, with reports you can read (not just stamps in the service book). the quality and condition of the tyres can tell a bit of a story: how worn, and are they good quality? cheap tyres suggests a car that is not 'no expense spared'.
i have a V6 GT, but no children. i love it. but i think i'd have a 4-door/wagon if i had children, say a 159 Q4.
