I don't think you'll find anyone that says Arctic is better than Noctua on a performance metric. Obviously the price of the respective products reflects that conclusion.
The only real component on a CPU air cooler that is measured in reliability is the fan. Arctic is more well known for having good performance at a low cost. Generally a failed CPU fan won't damage anything (the CPU will throttle if it gets too hot). It also depends on how many hours your machine is running for. If you can buy 3 Arctic fans for the price of 1 Noctua fan, does it make any difference if your stock Arctic fan dies? All factors that each person will weigh differently.