There isn’t one fixed “best” number. In practice, 3 bracketed shots is a common starting point, often spaced about 1.5–2 EV apart, and many cameras’ built-in HDR modes use 3 frames such as -2, 0, and +2 EV.

If the scene only exceeds your sensor’s dynamic range by a few stops, 3 shots is often enough. Some photographers use 5 shots at around 2 EV spacing when the brightness range is wider. Using very small spacing can create too much overlap between frames, adding little useful information.

More frames can help cover a wider tonal range, but they also increase capture time, alignment issues, ghosting risk, and post-processing complexity. If you capture an extremely wide range, you still have to compress it into a normal display or print range, which can make the final image look flat or low in local contrast if tone-mapped poorly.

So: use the fewest frames needed to cover the scene’s brightness range. Start with 3 exposures around 2 EV apart, then add more only when highlights and shadows still can’t both be captured cleanly. Also consider exposure fusion as an alternative to traditional HDR; it can produce more natural-looking results with less effort.