When swsh was in the process of being leaked, I initially felt like that Hatterene was the weakest of the hat line. Now, after seeing all the animations and such, I am now learning more towards Hattrem being the weakest design.
Hatenna is just too damn cute to not be the best of the three. It manages to successfully steal its cuteness from both the kirby franchise as well as from Ralts, while also combing a new weirdness into the fusion by making its party hat/nightcap actually a freaky tentacle tail.
Hatterene's design is definitely one of the best of Gen 8, as it ends up being so multifaceted. It's a fairy witch, that also looks like an alien that uses its hair to disguise its small body into the form of a much larger (and much more feminine looking) creature. It kind of reminds me of Beheeyem, where you have a pokemon that is clearly not human seemingly trying to look like it is human, rather than a weaker "monster just happens to look like a specific human stereotype/profession".
Hattrem compared to the other two largely lacks any of the inherent design weirdness, simply resembling a little girl dressed up with a witch hat and two large pigtails. While still adorable in motion (it has cute little leg kicks when its happy), the design just isn't as robust as either Hatenna or Hatterene. Plus I sort of wonder the reason of having Hattrem and Hatterene having identical bodies, kind of feels too redundant for a family and makes one or the other feel a little unnecessary.
