Too soon to say, as I discovered FAI a mere two months ago -- this, incidentally, could mean that it's a fleeting passion -- but CEV has definitely caught my attention, while the concept of a reflective decision theory I find really fascinating. The latter is something I've been curious about for quite some time, as plenty of moral precepts seem to break down once an agent -- even a mere homo sapiens -- reaches certain levels of self-awareness and, thus, is able to alter their decision mechanisms.