wah! middle of the nite u had an inspiration to buy a car so u
woke up and post here ah? 
anyway.. here is my take.
if the car is available from PI and AD, eg jazz/fit.. would be
better to buy from AD
if the car u like is only available from PI, eg toyota ist , then
it would be prudent to try and get it at the bigger PIs like eg.
richburg/ricardo.. it will cost more, but they r less likely to do
anything to jeopardize their reputation.
what kinda budget r u working with and which car(s) r u looking
at?