Doesn't really matter. The Switch splits large files up into 4GB sections anyway regardless on whether you have FAT32 or exFAT,. ExFAT has a chance to corrupt (as it has no redundant file table like FAT32 does) and has on legit Switch's on Pokémon Sword/Shield no less. Plus, if you happen to use a Mac, exFAT makes copying files onto the SD card a pain in the ass. If you're concerned about performance between the two, keep in mind that Nintendo doesn't use the same exFAT driver that mainstream OS's do, they use a shitty stripped down custom one that does a poor job. I'd honestly just stick with FAT32.