The tile with the stronger magnet is actually Picasso Tiles. The magnets in them are a little bit bigger, which is probably why they have a slightly stronger force.
I used all of my force to try to break these magnetic tiles in half, and the results aren’t too surprising: the Picasso Tile snapped in half and the Magna-Tile wouldn’t budge.
I think Picasso Tiles have a slight advantage over Magna-Tiles. If you want to bulk up on magnetic tiles, I’d recommend Picasso Tiles. And if you want to add in some really cool expansion sets and accessories, supplement with Magna-Tiles.