Well, as per my name, I like small characters, with a preference towards scalies, like Kobolds and Salamanders. I'm also a fan of Goblins and similar fantasy races, as long as I can keep 'em cute! As for color and design, I like simple designs for myself. My main gal Plum is a white-scaled Kobold with red ridges, and that's the kind of simple design I like.
I'm prolly gonna get some heat for this, but I've always preferred that anthro characters actually keep the traits of their respective animal (although if the designs are too animal-like it feels too close to feral for me, which I tend to avoid for NSFW projects). That means avians have only four limbs, with their wing doubling as hands, although exceptions are made for imaginary creatures like dragons. Non-mammals lack breasts; it just seems silly to me to put tits on something that shouldn't realistically have them. Any snakes are essentially nagas. I decided that arms of some kind would be a fair exception but putting on the legs kinda defeats the purpose of making a snake imho. If you're going to do that, just make a lizard. SHARKS SHOULD NOT JUST BE DOGS WITH FINS STOP DOING THIS PLZ. Sizes between species are kept mostly intact, though not to the extreme that Beastars and Zootopia do it.
For feral characters, it depends very heavily on what they're being used for. On one end my Warriors characters are very grounded in reality since at the end of the day they're just normal cats, while my characters for On The Origin are more eccentric with bright color schemes and behavior not typical for their species. Most of the time though some realism is kept intact.
Style-wise I like semi-realism the best because it keeps characters feeling grounded while allowing for some wiggle room when needed, (Are you guys seeing a pattern yet?) but really toony art is fun to do on occasion. S.O.S. has the most toony style out of all of my projects. Originally that was because it was a comic, and since it was my first I wanted the characters to be easy to draw. Now though I just prefer it that way.
When it comes to design elements I like, a blacklight/neon color scheme, especially with a good chunk of blue tossed in always catches my attention, even though most of my own anthro characters have natural color schemes. Chubby characters are something I like since I'm fat irl. Uncommon species are cool too. It's perfectly fine for people to make dogs, foxes, cats, sharks (which aren't really sharks but hnnnggg) and dragons but when I see an elephant, snail, fish, songbird, or frog that almost always gets an automatic favorite/like. Plz make more obscure species into anthros. I'm also a sucker for rainbows. I'm not gay or anything I just really like rainbows.
I don't really care for specific traits, I mean admittingly I love medival theme, but I have characters who are Sci-fi. Although admittingly EVERY character of mine can be adapted into other genres with minor tweaks and that's what I like, they can have a specific genre to be apart of but having them be capable of fitting in others like say replace their "frost blast spell" with a "frost gun" for fantasy to sci-fi.
I usually like to think of a theme I want, in some cases it might be "A Galatic bounty hunter who enjoys being a punk" which ended up creating my werefox boi.
I generally keep all anthro characters around 5', but vary so like a mouse would be more 3-4ft, whereas a bear woild be more 6ft, and what not.
Generally all characters have an outfit, even one of mine who 'prefers not to wear clothes' has an outfit, along with a husband who keeps him wearing something, even if it's pants torn up to be like shorts.
But one of the important things that all of my characters have is a form of backstory/lore to go with them. Everybody has a reason, everybody has a personality and have affected and been affected by the world and others around them.
I think that's one of the things I look for in a character, someone who has a story and not just "He's a coder who works in a store." Why did he become one? What does he do in his down time? What could I expect him to be doing when I don't see him?
Although admittingly this part might be more for RP, but... Even without RP stories are nice. Just RP makes it more required otherwise I won't bother.