gentler / more gentle / gentlest / most gentle

[Brazilian Girl]

I'd appreciate if the colleagues could help me with the adjectives listed below:

gentle, quiet, clever, simple, friendly

I found them as double form: gentle - gentler - the gentlest or more gentle, the most gentle, etc

Is it correct? Is one of these forms more commonly used?

Thanks for you help.

 

[Tegs]

gentle - gentler - the gentlest or more gentle, the most gentle.

All of these forms are correct, and they are used in different contexts, so I don't think one is more common than the rest.