Dash VS Underscore

Dash

• Dashes are recommended by Google over underscores (source).
• Dashes are more familiar to the end user.
• Dashes are easier to write on a standard keyboard (no need to Shift).
• Dashes don't hide behind underlines.
• Dashes feel more native in the context of URLs as they are allowed in domain names.

Underscore

Underscored_text is selectable as a whole by double clicking in some devices and long-pressing on mobiles, whereas with dash-separated-text the same actions select each
separated wordl --Titus

Reference

URLs: Dash vs. Underscore

Keep a simple URL structure