Choosing a character that is my favorite is not something that I can confidently do in the long term, because I am fond of all of my creations, old and new, and find different characters fill different roles within my writing, so I cannot honestly say that I have a set, all time character that I class as the best. I most certainly have characters that work better than others, especially in the sort of settings provided by RPGateway; in chat, a successful character that is fun to play will be very different to one that is successful and enjoyable in private. Also, a character that brings a great deal of enjoyment; for example one that is fun to play, may not actually be classed as the most enjoyable; sometimes, it takes a piece of dark, or gritty writing to get that sense of accomplishment. As well as this, seeing as I often operate in a mature setting, and have characters with little taboo, the age restrictions play into which character is most rewarding to play, as a censored or down-played character never feels quite so satisfying as one that is allowed to truly be themselves in a private setting where all those involved are connecting towards less socially acceptable behavior.
However, amongst my characters there are several that stand out from the rest, typically because they have managed to evolve far more detail in their timelines and personalities than others, or sometimes because they are easy or especially challenging to write. The most obvious choice for me would be Max, however, I find that he meshes poorly with both the Multiverse and a PG13 setting, so in this case I cannot deem him my favorite. He is also very challenging to play and takes a great deal of medical, psychological and legal research to maintain, which is not always conductive to good, fast paced, PG13 RP.
Michael on the other hand, is a little different. He was created on my original account here, several years ago now, and on the spur of the moment. He was made to join an ongoing chat RP involving horses and their riders, and originally he had neither back-story nor personality. He was allowed to grow, and as it happened he found himself partnered by an aggressive, uncooperative character; hands down the best thing that ever happened to Michael. The negative interaction allowed Michael's flaws to develop alongside (if not before) his strengths, crafting him into a imperfect being.
Designed to play on cliché to an extent, his story developed into something quite vast over a number of years and is still ongoing now, although he has abandoned RP almost completely as a character and ventured into the realms of the novel; one day, I intend to turn his story into something, but I have yet to find the correct amount of research on horses and time in my busy schedule. Michael will wait, and I haven't lost my love for him over the years, even if he's been annexed to an old, hardly used account and severed out of RP.