Cooling fan or a Rad system
Honestly, it depends on what you are doing with you PC. It also depends on your location in the world if it gets hotter or does it stay normal temps. Rad systems are great for those in the desert areas because it basically runs through a radiator and helps keep things cool. It depends on the CPU if you need a cooler or not also.
You would basically think that it is water when actuality it is not. You will end up having to replace the coolant in it every few months and keep it up on maintance it is not hard to do but it can be time consuming and can cost if you don’t have an AIO but if you go for an AIO you will not have to change it but it only covers the CPU not the GPU.
Cooling fans are prefect for areas that stay between 90 degrees and lower. You only have to change the thermal in them every so many months or years later depending on how much you use it and how hard you game on it.
If you have an high end CPU it is highly recommend you get an AIO because you will need a massive cooler for it if not.