Out of mine, it's Tak:

He's the first I created, and so he started out as the one I did everything to-- feeding, reading, training, etc. So by the time I got the hang of everything, it just made more sense to keep on spoiling him than to start over with a different gourmand or something :P And he's the most violent character I've got, so he would be the battler anyway. I also keep him as my active pet so I don't forget to switch over when I get an oracle quest and she can boost his stats a little. tbh he's not my favorite pet or anything, but I'm proud of his name (he was originally Tak the Outsider, and I snagged Tak in a clearing), and the Stephen King tribute items in his TC... so yeah, he's definitely the pride of my account. (And the Bloodred Serpenth art is PERFECT for the character the pet is supposed to represent - he's my favorite literary character of all time, so I'm super pleased with the color and species even after all this time!)
I just spruced up Tak's profile too, but I still need to edit his story a bit. It was the first chapter of a fanfic I never ended up writing... oops.
Somewhat related, the pets that are most special to me are Topper, Smiley, and Drifblim because they represent meaningful parts of my real life: Topper is a memorial to a beloved pet, Smiley was my childhood imaginary friend and favorite toy (still my favorite toy lol), and Drifblim is a beloved OC and plushie.
I don't think any of mine are pampered. A lot of them have stories and the ones who don't are just "pets". After I get all my stories out of the way, it's just looking for art that remains plus getting profiles made.
Alexia was my first pet, followed by Leeona. She was created after a RL friend. Even though we're not friends anymore, I can't bare to part with her.
I am pretty attached to all my pixels lol.
Oh goodness, in terms of "pampering," probably Zak. He's my gourmand pet. I am not a battler on here by any means, but he has the highest stats (literally everything is just above 100 lol). He's also had a lot of 'identity crises' because he's been so many different species and colors soooo does that count? Though truthfully, Chelsea is a close second. Several of my pets tie into each other but Chelsea is kind of the spotlight of all of them. She also has the biggest TC out of all my pets (which is again, not as impressive as other users).
I have more pets that I am much more fond of, like my pet Chili who is a tribute to my childhood dog, but I don't 'pamper' that pet much.
- I love that your most pampered pets both rhyme together. Tak and Zak. It's beautiful.
My most spoiled pet is Rourke. Just look at his freaking TC pfftt. I need to reorganize it again, but still.
Cynde Ever since my return he's been spoiled rotten.... trained vigorously, gets the best treasure items... got to be several good colors before I decided to keep him Storm. Yeah he's a brat but he's all mine. :)
widow. definitely widow. i can't really say why i've kept her around this long, i just really like that specific pet i guess lmao. she's been my active pet basically the entire time i've been here; she's had four name changes, and a pretty major species/color swap -- way back in the day she was a male nightmare kumos and now she's a very pretty glade tigrean.
i learned how to do fancy coding things mostly to make her profile look nice, and just about the only writing i've done in a long while was for her and cease (and her part was written first, then changed around for him all twilight/midnight sun-style lmao).
she used to have my biggest tc (200+), but while she doesn't anymore (grillby's 800+) it's probably the most expensive one (rip account worth). she also gets all the food, the books, and all the stat boosters; she's the only one i seriously autotrained (i'm way too stingy to do that with anyone else now, haha) and the only one i consistently train in the first place. i'm raising a couple of others bc i like winning extra loot but they're probably not going to see that much action p:
i love all my pets and i'm very attached to a bunch of 'em but if staff came down like, "choose one to keep, everyone else is being purged!" i'd pick widow over the rest of my horde ;w;
I first thought Anonymous would be my most pampered Pet, but after a bit of thinking (and maths...) I believe it's Joseph Oda. He has art worth over 200mil, story, Profile... everything.
Why? Hm, it just happened. xD
This is if I only count Art etc. Can't say anything about "Treasure Chest", though. In that case another Pet might get the trophy. xD
Riordyn, without a doubt! He's always had a huge TC (830+ right now), though not my biggest, and has been my gourmand for a while (3980) but I've gotten really into working on his stats lately, mostly for achievements and Sai. He's up to 1173 books read and slowly catching up all his stats to match his 500 Strength. Plus he's been colored Angelic... twice. Not to mention all the art he has.
Mine would probably be Schwarz, mostly because he was one of my first pets on this site, and I have a shit ton of time to spoil him than most of my other pets (TC, battle training, reading, gourmand). Also because it fits his character since he's godly, and has lived for sooooooooooo long to be able to accumulate all these experiences. Another bonus is I chose black (as what his names means) as his TC theme, which would be a lot more easier to expand.

def nivo lmao........ he was my first pet and is also my battler and gourmand his profile and tc haven't been touched since 2014 but i swear i'll........ get to it......... someday q v q
character-wise it's probably kizuki he's my favorite oc and also the one i draw and write the most |D
!!!! omg i remember drawing joseph 3 years ago god my art has improved a lot since haha
I believe it's good old Poseidon. He is my main battler and his treasure chest has a few more expensive items as well.
Art-wise I would say Colossus however I haven't linked anything on his profile at the moment.
In terms of subeta-specific spoils, I'd say it's either Knot or Bambi: Knot is my battle pet so I spend the most time on his training/books read, and Bambi is my (recently started) gourmand pet, so gets fed A LOT.
I try to spend fairly equal amounts of time working on pet profiles/treasures etc but I've definitely got soft spots for some more than others lmao.
Yeoman is my battle pet, so she is always in the resort, always in training, gets first dibs on every single book. One of my first pets! My actual first pet, Aariston, is also a lil spoiled, though I follow his character's personality and he does not battle or eat for the gourmand- though he is the pet I'm working on the pumpkin eater achievements with. :P
Sociopathy gets all the good books (battle pet) and Ariana gets the best food (gourmand pet). TC - wise I would say An-Dalkhu. His TC isn't the biggest one put I tend to pour the most sP/CSC in it.
Midnight. Not as much as she probably should be, but she has some stats + is the pet I feed and read. I've also put the most time in her TC and am pretty proud of it ;u; She's my favorite pet

My most pampered pet is definitely Dammath. He's my adorable baby boy xD. The first pet I ever made, and the first one I ever gave a potion to. He gets all the food and all the books (and love and attention) lol.
My most pampered pet is definitely Hector. He's my first born. The first pet I ever made or gave a potion to. He gets all the food and books first. The others get stuff too, but Hector gets everything first.
Fringie, first pet, originally named theFFRiNGE after a Neopet, which was based off an old nickname.
Just look at her stats.
LOOK AT THEM. Rank 779 as of rn.