Buying traffic can indeed be a daunting task when first getting into it. My suggestion would be to begin testing with a diversified portfolio. Start testing with solo ads/mailers, maybe some traffic exchanges, there are a few ad co-ops out there you can try...basically stuff like that. Also, I like to go with my gut and sometime try things out of the blue that don't seem to make sense. For example, I have spent money on sites that have a good reputation with flashy graphics, only to be terribly disappointed. Other sites I have tried with the most old school graphics have proven to be the most profitable.