I started out with Neopets like most kids did. I then moved on to MyEPets and LPS Online (think that's what it was called?) before I began playing my absolute favorite, Bearville. I'd still log on from time to time had they not shut it down.
My second favorite was Free Realms, which closed a little bit before Bearville did. I also had a Club Penguin phase in 2012 or so.
Other games I liked: Pixie Hollow, Fantage, that Mattel site with all the doll games and print-outs, and Disneychannel.com games. I'd also occasionally go on those shady "girls games" websites that are flooded with ads and bad quality games.
Games I never liked: Poptropica, Webkinz, Moshi Monsters, Roblox.