Stronger, as in which one would be less likely to break? I advise not worrying about it, I've used SRAM nine speed hollow pin chains for aggressive off-road riding, never had a problem. The only real difference is the weight, and even that is just a few grams. For a touring bike, I'd just go with the less expensive model since you're probably not concerned with a tiny bit of weight savings. If you like SRAM chains (and they are excellent chains), just go with the least expensive nine speed model, strength is a non-issue-