The difference between the two is negligible, .008" in bullet diameter, 10-15% in max bullet weight. Both cases are about the same size, both launch at about the same velocity. They are essentially two versions of a similar idea, one from the US, the other from Europe. 20 years ago my advice would have been to go with the 35 caliber due to bullet availability for reloading, but. 366" bullets are easy to find nowadays.
Never try to educate someone who resists knowledge at all costs.
But what do I know?