Want to bring a tripod?
A tripod is always handy as a photographer. Unfortunately, it does not fit in the bag, but fortunately there are bags where you can easily attach it to the outside. That saves lugging around an extra tripod bag.
Need to access your stuff quickly?
If you work in situations where there is a rush, you don't want to have to take off an entire bag first to grab your camera. Then you will benefit more from quick access to your camera from a sling or shoulder bag, for example. If you are in no hurry at all because you are mostly working on location or in the studio, consider a suitcase, trolley or backpack.
Do you walk a lot with the bag?
If you do a lot of walking, don't skimp on carrying comfort. Especially if your bag is heavily loaded, your shoulders and back will thank you at the end of the day. The best option then is probably the backpack. If you only carry the bag for small stretches, you can of course opt for a shoulder bag or suitcase. For avid hikers, a pocket or net for a water bottle is no luxury either.