They have different characters, so ultimately the choice will fall to what type of car you prefer on an emotional level. I suggest get the one that is in better condition, the one previously owned by a meticulous person. Another thing to consider: The V70 was a more popular platform, so there are more suppliers of parts, high-performance brakes, modifications, and accessories. The V90 may have typically been purchased by a more mature customer, who kept the car stock and took it to the dealer. Both have great engines. Good luck.