best is partially subjective, but mostly objective. Without knowing your case, it is hard to determine the best that will work with your case. I could, for example, suggest an AiO like the NZXT Kraken X62 or the Cryorig A80, but if it doesn't fit your case, forget about it. I could suggest something like the Scythe FUMA or the Cryorig R1 Ultimate, but if it doesn't fit your case, forget about it. Price is a good thing to know too. If the budget is, say, $50, that eliminates AiO coolers and the Cryorig R1 Ultimate from my example, and other options come into play. Also when you order can affect what is available and at what price.