The Best bag
These are just some thoughts to add to what others have already said.
First of all, as others have already said, there is absolutely no substitute to taking your equipment into a store and trying out a variety of bags.
Secondly, you may eventually need more than one bag for different situations. I generally have several bags:
- A bag when I am going out with a body and just a single lens. I use a holster style bag with a flap opening at the top and some room in case I upgrade my lens for something longer.
- A bag for a day out with the camera. This is larger and more flexible with space for additional lenses, a flash, additional batteries and personal items like a sweater and a notebook. I use a backpack style for this to spread the load but a sling style also works.
- A large bag for longer trips when I want to carry a backup body and lenses, a laptop, chargers etc. This has to be a backpack to carry the load.
For security reasons most of my bags don't look expensive and brand new so that they don't look too obviously like a photo bag. However, I have one smart leather bag which I use for weddings and other social functions when I my wife insists that I dress up for the occasion.
Don't think that you need to buy several bags now but it is worth remembering when you buy your first bag that it almost certainly won't be suitable for every occasion and you may need to add other bags later.