“Worser” may be found in archaic texts, but it is considered nonstandard and should be avoided in modern and formal writing.
When describing something as having lesser quality compared to something else, the correct word to use is “worse,” which is the comparative adjective form of “bad” (e.g., “The dessert was worse than the entrée”).
When describing something as having the lowest quality or condition compared to something else, the correct word to use is “worst,” which is the superlative adjective form of “bad” (e.g., “That was the worst play I’ve ever seen”).