when we do the design of bandgap , we normally take the tcf and psrr and line specs into consideration ! we can get the high psrr using the folded-cas amp ,but it will also introduce some offset , improve the area factor can reduce the offset at some degree! when you think about what is the amp archi you want to choose ,maybe you should choose it according to your design spec , eg: the design power dissipation and the supply power!