The larger the wall thickness (the second two numbers in the arrow size - 2018 = 20/64 OD with a .018" thick wall) the more durable the arrow will be to bends and dents. So a 2018 will be a little more durable (and heavier and stiffer) than a 2016 arrow. A larger OD will also make the arrow more durable (and heavier and stiffer). I have used 2115s quite a bit and find them to be very durable, but not indestructible. When stumping, I like using HTM rubber blunts over a steel blunt (gives you a very heavy point weight). I pull the rubber blunt off a little and away from the steel blunt to give it a cushioning effect if I hit something really hard. With this setup, these arrows will take quite a blow and lots of abuse. An aluminum arrow flying sideways from a glance can be vulnerable to bending.
But since I have a straightener, I can salvage many of the bent arrows and use them for stumping.
I like XX75 and XX78 alloy aluminum shafts. If you buy cheaper shafts, expect to be disappointed with their durability. You NEVER get what you don't pay for, especially with aluminum arrow shafts.
That's my $.04.
Doug