If you want an classical single key paper wallet, then I would simply use Core on an airgapped computer to generate a private key and then copy the private key and address to a piece of paper to be printed with a dumb printer. I prefer to use seed phrases to generate HD wallets, though, rather than individual key pairs. For this I would either use Electrum, or generate the seed phrase manually by flipping a coin. Write that seed phrase down, and then use Electrum to derive the relevant addresses from that seed phrase to either also be written down/printed off, or transferred over to an online machine via QR code. Once you have the seed phrase written down and some addresses to send coins to (and double checked everything!), you can wipe all traces from your airgapped computer.