We look at the top models in two categories: big wall and self-rescue and emergency ascenders. Climbing El Capitan and getting your buddy out of a crevasse are two very different applications. Below we outline which device is best for what and which ones can do it all.
The Best Ascenders for Big Walls and Rescue
The Petzl just barely edges out the BD for our Editor's Choice. We love both of them. The Petzl wins because it's a little lighter, a fraction smoother, and Petzl outlines many other uses from self-belay to rescue. Black Diamond does not detail using the Index for self-belay or rescue in any of its documentation. In the latest update to the Ascension, you can now clip two carabiners to the bottom hole and thread the gate of most locking biners through.
The downsides, other than being expensive, is the handle comfort. Some people love it. Other people find it digs into parts of your hand, unlike the BD handle which doesn't have sharp points. Again, this is personal preference and most discomfort issues are solved with climbing gloves, which most people use anyway. Overall, this is the best, but if found the BD on sale, we would probably grab that instead. The BD is also $5 less per hand or $10 less for the pair.
Also One of The Best
Black Diamond Index
The Index is a significant improvement over BD's last model, the nForce. It's similar to the Petzl Ascension with the main difference of a "trigger finger" option where you can use your index finger to pull the cam back (but not entirely take it off the rope). It arguably has a more comfortable handle than the Petzl.
There are no significant downsides; everything is a nitpick. It's heaver than the Petzl and not quite as smooth. However, the smoothness could be related to experience: we've been using the Petzl Ascension incarnations for decades and have less than a year on the BD. Overall, this might be the best big wall ascender out there, or 2nd best, it's personal preference.
Best for Emergencies
Sterling Rope Hollow Block
Whether multi-pitch climbing or skiing in crevasse country, the HollowBlock is a light and effective self-rescue tool. It's a 6.8mm Super Prusik that is lighter, stronger and more convenient than a standard prusik. It works on thinner ropes than most mechanical ascenders. While it's more expensive than making a prusik out of accessory cord, it's much cheaper than alternatives like the Ropeman or Tibloc. It doubles as a sling.
The downside to this and any prusik is that it typically takes two hands to move if there is any slack in the rope. It also doesn't attach and re-attach quite as fast as a Ropeman or Tibloc. On icy ropes, it doesn't have the same bit as an ascender with aggressive teeth. But all those are minor things that may not affect your use. Overall, it's a great item to have in the mountains.
Wild Country Ropeman 2
The Ropeman has too many uses to list here. It can be a critical part of your self-rescue kit, a backup, and hauling device, part of a self-belay system, and used, by expert climbers, for simul-climbing. It so light and compact that it arguably takes less space than a prussik as an emergency tool you always keep on your harness.
Other than being expensive, that main drawback is that it requires research and knowledge to know which set-ups it can be used safely in, especially if used in a self-belay system. If you are just starting to climb, it's better to master the prusik first.
Unlike a harness, where you can get a sense of how well it will work based on hanging around in it, there is no easy way to test ascenders in a store. The reason is that ascenders are not intuitive to use at first. They take practice to move efficiently and get on and off the rope. So more important than holding these in the store is asking the opinions of experienced climbers.
Left and Right
The Index and Ascension are sometimes sold individually, not in pairs. So make sure you are buying one right and one left.
Ease of sliding up the rope
Of all the features to look for, this is the most important. It is how easily the ascender slides up the rope that will determine how tired your arms get over time and what systems that it is best for whether its big walls or crevasse rescue. If the device slides up effortlessly, your arms will thank you.
Ease of taking on and off the rope
This is the second most important feature. No ascender is intuitive to use at first; it takes practice to be able to quickly get them on and off the rope. So if you are testing ascenders head to head in the store, make sure you use them a LOT.
Weight is not a big deal when you are using ascenders. But you will notice the difference in weight when they are clipped to the side of your harness.
Every model we covered here is the best at something. It all comes down to your activity and preferences.