For most puzzles I reach for the six-letter fill 'ELATED' as my go-to — it's the crossword workhorse for 'overjoyed'. If the grid gives you six squares, ELATED almost always fits the tone, the letters are common, and constructors love it. If the pattern suggests eight letters, 'ECSTATIC' is the natural leap: it carries a slightly bigger emotional boom and matches longer slots well. For a tight four-letter slot, I check whether 'RAPT' could be intended; it has that older, literary flavor and crops up in British-influenced clues.
I also like to walk through the thought process aloud: scan the crossing letters first, then match the intensity. If the clue's surface hints at a very high degree — words like 'utterly' or 'simply' — lean toward 'ECSTATIC' or 'EUPHORIC'. If the clue feels casual or contemporary, 'THRILLED' (eight), 'GLEEFUL' (seven), or even the colloquial 'OVER THE MOON' (if the puzzle allows multiword entries) are possibilities. In quick daily puzzles you'll usually see ELATED or RAPT; in themers or themed Sunday grids, constructors might prefer the flashier ECSTATIC or EUPHORIC.
I like picturing scenes from books when choosing fills — someone receiving a long-awaited letter in 'Pride and Prejudice' might be described as ELATED rather than ecstatic, which feels too modern. That little linguistic instinct helps me lock the right word. Personally, ELATED still gives me the most crossword joy when it clicks into place.