discernible but inconclusive
On the left: ten months old, and worn solidly for the first nine of those months. Silent until the hole into the inner workings was exposed, after which they squeaked and sucked or hissed depending on the dampness of pavement.
On the right: sixteen months old, worn solidly for the first seven months until the cushioning collapsed. Resurrected a month ago when those on the left started squeaking. Have now started squeaking themselves and making squidging noises in wet weather.
Though those on the left were (after much searching to find something suitable which wasn't yet another pair of those on the right) comfortable and lasted slightly longer than those on the right when those on the right were reinstated the difference in comfort (even when the heel-bounce has entirely disappeared) was remarkable. Those on the left have the advantage of drying out much more quickly than those on the right. Those on the left still have their original laces whereas those on the right are on their third set. Those on the right are noticeably grippier, especially in the damp. Those on the right are slightly wider and shorter and thus more my-foot-shaped. Both cost approximately the same.