This is difficult to answer in a generic way, because it depends on things like your investment/trading horizon, the phase (bullish/bearish/neutral) of a market, as well as the individual market itself.
As a general rule though, you should actually look at more than one time period, and more than one time scale (daily, weekly, etc) – starting from the highest scale and working your way down. This is the most effective way to get a robust sense of a market’s current context and directional bias.
We find that 250 bars (the default) is a good general-purpose starting point for most scenarios, but you should experiment to see what fits each market and your objectives best. Also see the section: Before running an automatic wave count