* Comparative: Genter (although less common, this is the technically correct form) or More gentle
* Superlative: Gentlest (again, the technically correct form) or Most gentle
While "gentler" and "most gentle" are the most common forms, it's important to note that "genter" and "gentlest" are technically the correct comparative and superlative forms according to traditional grammar rules.
However, "gentler" and "most gentle" are widely accepted and used, so using either is considered correct in most contexts.