Leather is excellent because it lasts well and it breathes. Check the stitching for neatness and regularity. The outer sole should be fairly firm. Avoid very soft, cushy outer soles that you can easily dent inwards with a fingertip you need solid support more than the feeling of walking on a mattress. Soft outer soles do not support, stabilize or protect, and the material tends to break down quickly with use.
Some running shoes work well for walking.
In fact, some shoes advertised as walking shoes are not good for walking at all, so judge by the above criteria. Some of the running shoes made for light training or racing are suitable for walkers and racers.