What do you mean by learn your key by heart? Memorizing the seed(s)? That's not a good choice. Even if you can remember the mnemonics with some tricks, nothing guarantee that you can remember it tomorrow. Printing the copy is better as you mentioned, as long as you store it securely. Buying a wall safe is probably a good idea but I won't put it open where people can see it as if you tell people "hey, there is something valuable here".