I'd also recommend going for an RA job unless, like winnie said, you can get into a funded master's program with a good track record (or you have money to spare--you do NOT want to start a PhD program in any more debt than necessary). I have a friend who went to Villanova and she was fully funded and is now in a good clinical doctoral program. I don't think that the master's degree gives you a big enough advantage to be worth paying for. People with masters don't usually get a huge amount of credit for their coursework once they're in doctoral programs-- maybe they'll get out of stats, and if they're really lucky their thesis might transfer. Most masters programs are not at schools with PhD programs, and I have the impression that PhD programs that do have masters programs associated with them (e.g., American, BU, Drexel, etc.) don't regularly take their own master's students (not that it's impossible or anything, it just doesn't seem like there's much of an inside advantage). Masters programs tend to be much bigger than the PhD programs and once you apply you're competing with all of the hundreds of outside applicants as well. Also, masters programs (esp at schools w/ PhD programs) tend to be regarded as cash cows (which in many cases they are).
I didn't get a masters before grad school, so if anyone more knowledgeable out there wants to dispute this information, feel free.
If you do go the masters route, in addition to looking for programs with funding I would recommend 1) looking at programs without PhD programs, so you don't have to play second fiddle to the doctoral students, and 2) definitely going to a program with a thesis requirement.
I think the RA route is better (that's what I did) because you don't have to pay tuition and actually make money, and you can get many of the same benefits as you would from a masters program (e.g., good recommendations, publications, presentations, research experience in your area of interest, and often times training in assessment techniques and other relelvent skills), plus the added maturity of being out of school and in a work environment.