On the surface, this looks like no contest. Surely the walker is easier than the crutches, right? Um, not so fast.
I've discovered the opposite is true in certain circumstances. Since I have a strong upper body, the crutches allow me to use some of that power, enabling me to go farther without rest. The walker (technically rollator in my case) is great for when you need to sit to rest (just turn around), but since using it does not require arm strength, all of the energy to walk has to be supplied by the legs. Meaning it actually tires me out faster.
Now I'm not saying that one is better than the other. But if your legs give you problems that require extra support, try both, you might be surprised.