Probably yes it will be the best way since it can be accessed and used almost anytime since it is flexible. However the cold storage or hardware wallets have more security than of the online wallets, even though they have their own private keys you still can't be sure when will the 'hackers' will attack you so I recommend to use hardware wallets (extremely recommended if you have large amount of Bitcoin or converted cash). But if you just have a few amounts and just wanted to be used in your everyday transactions then online wallets are more versatile to use.

To add to yours, after writing them on the piece of paper you can either dig the ground and save it inside a box under the ground or better keep the paper in a personal safe or bank safe and I'd say that's 100% secured.

New notebook with SSD 240GB.
Bitcoin-core 2014.
No any other software.

Well the safest ways are probably using cold storage and some examples of cold storage include the following:

1. Using a hardware wallet which is usually something shaped like a USB that you plug your computer to send payments, some really populare hardware wallets include Ledgerwallets and Trezors.

2. Another example of offline wallets would include using a paper wallet which is a document that you can carry around that has everything to use your wallets, etc private keys etc.

3. Something else that would be an offline wallet would be to attach bitcoin to something physical such as physical bitcoin but they are not mainstream and less  safer than your other options.

Here's a guide by Ameer Rosic that provides great insight and answers to your question:  https://blockgeeks.com/guides/paper-wallet-guide/

If I am not wrong, then Coinbase was hacked earlier. Also, who is stupid enough to keep their coins in an exchange wallet?

Oh god no pls

There were lots of articles regarding this. Although, there is no possible another application that can hold BTC, they usually get hacked by experts. The best thing to do is to widthdraw BTC in form of our currency then make account in a bank, for future investment.

The safest way is to download the full wallet or at least like exodus and keep it in secure machine, may be separate machine that wont be connected to internet or a virtual machine (without internet)

Really, it is your choice wherever you are more comfortable.

I could only make suggestions on how good the wallets are but not take biased assumptions out of it. But since this is a question out of curiosity and opinion I will have to make it brief as possible.

I would suggest not making only one kind of wallet but different kind of them. Every wallet has its own advantages and disadvantages, but when you're only concerned with security then - having online wallets is quite good if you ask me. I has its own security measures just make sure to confirm everything when you use it. And then there is also a cold storage or what we call hardware wallet which has pretty much have more security than any other wallets (I'm not saying that it has no disadvantages in security). Unlike online wallets it is offline and will be stored in your PC. Just take note that if you support it with your PC having also the maximum security (like Mac) then it will be the 'best' to store it anyways.