You will not like my reply.

I am going to assume you are planning to store what you consider to an un-lose-able sum.

Personally I think using moneroaddress.org is risky unless you know exactly what you are doing, and then the Dunning-Kruger effect is your enemy. You should ABSOLUTELY NOT use it on a computer that is connected to a network, or ever will be again.  If you can use some disposable OS or tails etc on a laptop that wont ever...  muh seriously.  It's really really just a bad idea.  I assume you will be entering in seed words on a internet connected computer...  all it takes then is a keylogger etc.  I guess if you are going to create a watch only wallet that is basically cold storage...  Then it's better.

Yes MyMonero is (probably?) trustworthy.  But you are choosing the lest secure of all Monero wallets.  It's a web wallet.  I would either use the official wallet, or Feather.  And you might as well generate your keys in those if you planned to just type them in in the first place.

Using a hardware wallet is really the best bet.  Period.  Seed created on unconnected device.  Stored on paper (or metal etc).  You get to use a Bip39 passphrase...  It's worth the 60-100$ IMHO.

Maybe someone can give you a less paranoid answer...  Why says I am right?  Don't trust.

Good luck!!!