Side pockets are a useful addition. Plastic or metal camera cases are more resistant to abuse, but unless your camera bag will be on the bottom of a luggage pile, they are usually less practical than soft cases. You take a chance in buying a camera bag by mail order because you don't get to handle it beforehand to check that it will hold all your gear, try its weight on your shoulder, test its zipper and snaps and so on. If the bag looks used but is still serviceable, thieves might think it contains older, less-valuable camera gear and pass on it. Examine all of a bag's features to ensure they suit you.
Most photographers find two bags more practical than one large one.
If you have a lot of gear to haul around, consider more than one bag, in sizes suitable for different situations. Some camera cases are completely waterproof , if that's what you need. Make sure to get the right one for your climate and shooting conditions. You have to set the bag down to remove items. Like a suitcase, everything has to be stored carefully back inside before you can move on.