Considering their prices, I'd say none. I'd rather buy 128GB cards right now, as they cost about 1/5th of a 400GB or 1/7th of a 512GB card. A 128GB microSD card costs only about 20€, but a 400GB about 100€ and a 512GB card about 150€ right now, so neither of those are really worth it.
The Nintendo eShop rating Thread: http://gamrconnect.vgchartz.com/thread.php?id=237454
The Steam/GOG key gifting thread: https://gamrconnect.vgchartz.com/thread/242024/the-steamgog-key-gifting-thread/1/