There are some obvious choices but to get all the data together would be a daunting task. As soon as you name something as flattest someone else will come up with a different bullet combo that will out do it. I know trajectory is only one item for mid to longer ranges and that it is almost moot for scope dialers and long range target shooting but for point and shoot types I am curious about the rankings. To put it another way which cartridges are better for this than the 257 Weatherby?

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli