This isn't that complicated.

The answer is, simply: ED25519 if you're using modern services that support it.

or RSA (4096 or at least 2048 bits) for services that cannot handle ED25519 (including AWS -- yes, still, even in 2020.)

So you should probably generate both to cover most possible scenarios:

    ssh -t ed25519      # for most purposes (not AWS)
    ssh -t rsa -b 4096  # for when you're not using something like Userify