Choosing a camera bag is a personal decision. I suggest visiting a camera store and looking at what they have in stock. I personally like the Domke bags, which I've been using in various sizes for over 30 years. But if I had never seen one, I would only purchase it from a mail order store that had a good return policy. That's why I recommend visiting a camera store.

I think you may find that you need more than one camera bag, depending on what equipment you want to take with you on any given day.

Larry is correct. Check out the bags in a well stocked store.

I have a number of bags -- backpacks, several sizes of shoulder bags, fanny pack bags, and, believe it or not, several diaper bags. First, a backpack is a great way go carry a load, but very inconvenient when you want to change a lens or get film which is in the bag. Shoulder bags are often too heavy to lug for a day, but easier to get into -- and out from under. Diaper bags are very inexpensive relatively and some are very well made. I have an "Eddie Bauer" man's diaper bag which has a great appearance, plenty of pockets, waterproof (at least from the inside) and was only about $20. I have a "Winnie the Pooh" diaper bag which I sometimes use when I am going places where something could be stolen -- no thief really wants to take a chance that it is filled with dirty diapers. Fanny or waist packs are very convenient, but often too small.

Back to Larry's suggestion -- Bring your equipment to a good shop and see what size you need and what works for you.

Dave