Whether you must wear one by law is not really the issue. You should always wear one that is at least DOT approved. The price of a helmet doesn't tell you how effective it will be. The higher priced ones generally have more features, may be lighter weight and have a better finish. All DOT helmets will protect you.
Many people recommend full face helmets.
For the summer I wear the DOT approved shorty. You will notice both have visibility enhanced with DayGlo and refelective stickers. Your new helmet should fit semi-snugly, not be loose. The fit will loosen up a bit as you wear it. Those lids so many people wear are nearly useless in a crash.