I joined both sites the same time and after playing on them for a month chose Its Your Turn. Personally I think they are both good sites with different strengths and weaknesses. I like the fact you can see who is on line at BrainKing and I find the grading systems an interesting gimmick. I however prefer the way the tournaments work on Its Your Turn and, for me at least, is a more robust site with less crashes.
I don’t like the rule on Brainking’s Espionage that allows backward then forward but not the other way around. This seems to penalise positive play. I prefer Its Your Turn’s approach that you cant go back where you came from at all.
Little Golem is a great little site as well but limited games.