Street or sidewalk is entirely situational. There are times where I'll do either based on the time of day, where I am at, etc. Safety comes first for you and those around you and if you can't ride safely on either you shouldn't be there regardless of the law.

If you do happen to be on the sidewalk you are a guest there. Everybody else gets the right of way. Ease up to intersections because vehicles are not used to the speed of an approaching bike and their quick glances don't account for it.