Exactly why I use my front waist bag. Makes getting to the equipment 100 times easier and faster than a shoulder bag or backpack.If you won't need to swap lenses a lot, backpack should be the best to carry gear around, in a more comfortable manner than sling/messenger/shoulder bag.
However if you would swap lens a lot and very frequent, backpack would not be your best option.
I have a few backpack style camera bags, 4 to be exact if the usual hiking backpack w/ camera insert be excluded. They are in different size for different purpose/event. However as I am using a 3 lenses setup (an ultra wide zoom, a standardvwalking around 35-70 and a long zoom), I swap lenses a lot. If I would carry a backpack (for various reasons), I have to carry an extra small shoulder bag (good to carry 2 lenses) for my lenses swapping.
My 2 cents.