You want to consider the size, durability, and material. Firstly consider if it is too big for your dog to hold, or too small and could be a choking hazard. Durability needs to be considered in terms of whether your dog is a heavy chewer or not or whether they have strong jaws muscles. As for material you need to ensure it is not toxic and is safe for your dog. You can provide them with a few different safe toys to find out which are their favorites. Once you have found the type you can choose the best of that type.