If you had all the resources in the Minecraftian world, what would your mob grinder look like? Mine would use infinite villager breeding and a zombie spawner. On command I would be able to let the zombie turn the villagers into zombie villagers and be ripe for my slaughtering.
That has actually been done, its was by TangoTek. https://www.youtube.com/watch?v=MdXdtGR0JhE&list=PL8t707flkqpe7HptgA3dVssoiofDa6uMN&index=4
Mine would have spawner a for all mobs. The I would build a massive system that would allow you to make a certain kind of mob drop. The it would have an auto kill mechanism that would drop a peice of TNT to kill all mobs in the killing area.