Both 日没 and 日落 express sunset but which one is often more widely used?
日没 is more literary. You are more likely to find it in novel. But not in day to day speech
日落 is more colloquial and common in text
Japanese also use '日没' (にちぼつ) for 'sunset'
In practice, if you say "ri4 mo4", I would think you mean 日末("the end of the day"), instead of 日没. 日落 is the common word for sunset. Never seen 日没 before.