The Big Mom Pirates are my favorite Yonko crew, I like how the foundation of the crew is from Big Mom's own family, and I also like each of the members own unique designs and personalities. When it comes to the officers of the BMP which are Big Mom's children I really like how Oda gave each of them very unique designs, and that's something he didn't have to do. Most of the children only play minor roles and yet despite that Oda decided to give each of them very unique designs, I also like their different devil fruit abilities which makes their powers very diverse.
Big Mom with her soul soul fruit can create an army of homies, Daifuku can summon a genie, Mont-d'Or can control and manipulate books allowing him to do stuff such as trap people in illusions or even put someone inside the book. These are just a few examples of the diverse powers of the BMP, I also like how each members are decent fighters even if not all of them are super strong knowing stuff like haki and even rokushiki specifically geppo.
I also like how they are themed after fairy tales and fantasy fiction such as Alice's Adventures in Wonderland, Charlie and the Chocolate Factory, The Wonderful Wizard of Oz, and many more. I like how the colorfulness of the crew masks the violent nature of the crew, this is a pirate crew you wouldn't expect to be very violent when you first meet them. The way they look and how colorful they are is a perfect facade for their violence, I also do like how the crew is very good at trickery and deception such as Brûlée using a mirror image of Sanji to lure Luffy and the others into the seducing woods or even having Cracker make it seem like Luffy actually punched through him.
The country that they rule over which is Totto Land is another thing I really like about the Big Mom Pirates, Totto Land is a country themed after foods and seeing how there are 35 different islands in Totto Land you can pretty much choose any of the 35 islands to live on such as Wheat Island, Candy Island, Potato Island, and many more.
Overall I think Oda did a very good job with the Big Mom Pirates from their designs to their personalities to their powers, everything about them just feels very unique.