Which one do you recommend?
Aegis for Android, Tofu for iOS.
I prefer to keep my 2FA in the cloud in case I lose my devices
Then you should stick with Authy. Backing sensitive data up to the cloud is a bad idea, and backing 2FA codes up the cloud is an even worse idea, but if you want that functionality then you'll have to stick with Authy to do it smoothly. Good 2FA apps do not back up data to the cloud, instead supporting local encrypted back ups only. You could always upload one of these back ups to the cloud, but I wouldn't recommend it.
Can I keep my backup codes in Aegis servers?
Aegis does not have servers. It is all done locally, which is by far the most secure way of doing things.
Authy is amazing for me, because I keep my 2Fa codes in my android and in my windows devices. I just disable new devices, and I feel very safe about it.
But you place full control of your 2FA codes in the hands of a centralized authority.
Can Aegis disable new devices?
There is no way to "add" new devices without having access to your 2FA app or one of your backs up to copy the shared secret(s) from.