Spark plugs. Why is it so hard?

Why are there so many plug choices? What parameters are most important? For example, my trick flow heads call for auto lite 3924 plugs. But nowhere else do I find them for mopar big block. I saw @AndyF recommend NGK plugs I think 6987. But they are not 440 either. Is it the heads, the block, the ignition, or what else? I have a efi sniper, 512 with hyper spark ignition and I have used the auto lites but wonder if they are correct for the application. Any guidance appreciated.