There are several separate factors you need to consider, but at the end of a day, you need a long blade, flexible design, and you also need an exceptional edge. The blade must be perfectly serrated, suitable for slicing soft bread without ruining it.
Your new bread knife will also be reliable and durable. They are generally immune to corrosion, but not as other knives. After all, they are not designed to cut through fruit and vegetables or meat.