I've got a few favourites in each town I've got. I like the EA-made characters due to their backstories most of the time but sometimes it's got to do with their roles in my game(s), too. I'll list a few off the top of my head below. I've recently got into the habit of placing my own sims in custom neighbourhoods and so far it's been entertaining, knowing the background I gave those sims when creating/playing them previously.
Sunset Valley, - Agnes Crumplebottom, Bella Bachelor, Mortimer Goth, the Frio brothers.
Twinbrook, - Sofia Carlton, Anna-Liza Riddle.
Barnacle Bay, - Odessa Cross, the Caliente sisters.
Bridgeport, - Matthew Hamming, Elvira Slayer, Lotta Greaves (deceased).
Hidden Springs, - Liam O'Dourke, Francisca Vanderburg, the Shue family.
Appaloosa Plains, - Gracie Loveland (best friend of probably every sim I placed in that town), Benjamin Schmidt, Gavin Pinkerton, Calvin Riffin.
Lunar Lakes, - Amelia Loveland. I haven't explored this town much yet.