It all depends, honestly. Am I going to put it on my horse? Am I going to put it on the mobile hat stands with which I will eventually share my house? Am I going to wear it myself?
For my horse, the absolute winner, hands down, is the Top Hat. Some of my other faves include the Hair Bone, either the Lucky Bow or Polka Bow, and Bowler.
For the kids? I really like the Witch Hat and Skull Mask, turning them into Shock and Barrel from Nightmare Before Christmas. In another save I joked about how my kids needed all the help they could get to survive what with me working and my spouse off doing random crap so I put them both in a Golden Helmet each of them.
For me? Well... it depends on the aesthetic for the character. I want something that fits the motif. Eventually, in most of my long-played saves, I end up getting one of the magic hats from the Desert Trader, whichever fits the rest of the outfit (or in other words, which hat I pick is based on whether I'm wearing prismatic pants or prismatic genie pants).