Pannier bags are great because you can hop on your saddle without having to lug anything on your back. You can almost forget about this style of commuter bag whilst cycling as they are kept out of the way.
The downfalls are that not every bike is pannier rack compatible and the bag can’t be opened and accessed easily on the go. If you’re looking for something to hold larger items then the pannier bag is your best bet.
Have a read up on some of our pannier bag reviews if you’re looking to buy: