This morning the clue 'pinnacle' had me grinning—it's the kind of one-word clue that begs for a classic, compact fill. My first instinct was 'ACME' because it's crossword shorthand for 'highest point' and shows up all the time in weekday puzzles. Four letters, vowel-consonant-vowel-consonant, and it fits nicely with a lot of common crosses like ending -E or starting A. If the grid has a third-letter 'M', you've basically won.
That said, I always keep alternatives like 'APEX' and 'ZENITH' in my mental toolkit. 'APEX' is equally common in short slots and sometimes favored when a grid designer wants a less cartoonish vibe than 'ACME'. 'ZENITH' is longer and more elegant—if the slot's six letters, that's often the go-to. 'SUMMIT' and 'CLIMAX' are also contenders depending on tone and letter count.
In practice I check the crosses before committing. If a down clue gives me an A as the first letter, 'ACME' or 'APEX' becomes very plausible; if the pattern is E N I T H, then 'ZENITH' locks it in. Personally, I love how a single clue like this pulls together vocabulary, tone, and crosswordese history—solving it always makes me smile.