Obviously anything comfy is cool - some prefer running shoes as they are often designed to give the wearer that bounciness on impact, others prefer any old tat.
I guess tennis shoes would be designed to achieve a similar effect.
Don't pay too much, you can easily find good quality shoes for exercise. Maybe stay away from the bigger names and get something from the less popular brands as their prices are lower, they look practically the same and the quality is the same. Good luck.