Here's my two cents... I'm currently finishing up my MS degree in psychology, and I am definitely in favor of getting a masters... it helped me out a lot, not only in figuring out what I wanted to research, but also in preparing me for upper level work. I'm totally Pro-MS!
So, of course, I would suggest MS over an MA if you choose this route. The reason being that research experience is much more valuable than clinical experience (which they don't care much about at this stage because they're looking for fitting you to a lab) or other graduate course work (which you'll probably have to take over in the doctoral program anyway).
I've gotten 6 interviews for School Psychology doctoral programs thus far and one acceptance already, so I haven't felt a bias against master's students. My stats are comparable to yours (my GRE slightly lower, my GPA slightly higher), as well. I also had 3 years of undergrad research experience, but it didn't line up with what I wanted to do afterward, so I felt a bit lost. Not sure where you're at, though.
Additionally, when interviewing for doctoral schools the main focus has been on my research experience at my current program... so far it's only been a plus that I have experience in grad level research. What's really helpful is that I was able to integrate my work into my current research interests, so it helps to "sell" why I fit so well... not only am I interested in it, but I actually have done work like it. Obviously, you know already what you're interested in researching, so if you go into a master's program I would suggest you team up with a professor that will help you gain experience in that area to make you a stronger fit. Like everyone is saying, fit is everything! Also, my thesis comes up a lot, and it's a big plus to say you've been in charge of a study... especially when doctoral programs have master's type projects en-route to the PhD. Many interviewers have said my thesis could either substitute for this requirement or that "well, you're already well prepared to deal with this when you come in, so you should have no problem with it."
As a side note because it's pretty rare, but there are a few master's programs with some funding, I was lucky to get an assistantship (about half of what you get for a PhD program), so it's still a decent option to try for! That being said, it may be easier to get an RA if you find someone that lines up with your interests. All of my previous comments are still valid if you get more research experience. Plus, it will certainly be cheaper. Otherwise, I agree with what else has been said... focus on fit!!