I often have hard time concentrating on things myself, so the more compact and simple the layout the better! I love wikipedia-style formatting where I can already sort of expect to see the basic information on either left or right, oftentimes under a character image, and I like it when the information is also consistently arranged (personality, appearance, history etc). I have come to notice the more ADD and/or dyslexia friendly the layout is the more I also enjoy reading them, even though I do adore very busy, colorful and nicely decorated profiles as well - I just find the former easier to read. I also like narrow-ish boxes solely because my screen is very large and my eyes often accidentally jump over lines or words if I have to read from a large area. I also know a lot of people might not necessarily be big fans of smaller fonts, but I do enjoy them when they're still big enough I can read them without squinting.
In general though, I'm super fond of layouts like this one by @watergems and use it myself, as I find it simple and clean enough!
I also really really like it when people add small images to the profiles, like I don't consider it a necessity by any means, but little things (when arranged nicely) really bring more life to the profile and help me focus better. It's especially effective when there is a lot of text so I can use images placed among the text as a "bookmark" of sort to know where I'm reading, and also to make the amount of text look perhaps less like a wall of text? Not that I really mind that either, as I'm guilty as charged of having those haha.
In terms of content I actually love it when people write a lot, especially if it's combined with an easy-to-read layout! If I like a character I naturally want to know more about them, so being able to access that information always feels like a treat ;v; I don't use likes/dislikes function myself because I feel like they'd make my bios a tad too long, but I really like reading those sections, same for trivia.