Depends what you are doing. An Olympic weightlifting bar is (men's) 20kg with a 28mm grip  while a women's bar is 15kg and has a 25mm grip. The steel and grip diameter affect the whip of the bar which is huge in oly lifting. They also (good bars) have multiple bearing so they spin fast and smooth. Super important when you are trying to get under the bar.
Powerlifting bars are (men's) 45lbs and the grip is thicker. Because they are larger, they don't have much whip and are way stiffer. Good for really heavy squats, benches and dead lifts, but bad for getting from the ground to overhead. Spin isn't nearly important.
The bar does matter, just not to 95% of people lifting on NS.