Your breakdown by decades narrows the field. I really think of Killebrew, Carew, and Mauer as something other than first basemen, so I would not choose any of them. All three are obviously great baseball players, but I don't think of them as first basemen. Next cut...Mientkiewicz was awesome, one of my favorites for those early 2000s teams, but simply not as good as Hrbek or Morneau. I lean toward Hrbek, but the 1980s Twins are when I really started paying attention to the Twins. Am I just choosing that era and Hrbek nostalgically? Morneau seems like he had better annual numbers but for a shorter period of time. My deciding factor will be World Series championships--therefore Hrbek is the man!