If you're interested in simply making some bitcoin, Predictious might be a good idea because the low volume implies mispriced contracts. (Similarly, I think if one carefully studies Betsofbitcoin in detail, it may be possible to make steady profits off it: the rules are so bizarre that there must be inefficiencies.) Another advantage of Predictious is that it's operated by Pixode, which seems to be a reasonably legitimate company (more than one can say for most things in the Bitcoin space).