I don't know that there's a 'best' route, but there are definitely more tested ones. Getting a masters first is not really necessary. It won't hurt you, but it won't necessarily make you a better candidate. It's a great route if you don't have the grades to get into a doctoral program, or some of the other reasons listed above. BUT there are considerable downfalls: you typically have to pay for masters programs (so consider the loan $), and you quite likely will have to repeat at least some if not most coursework and quite possibly do another masters thesis once you get into a doctoral program (particularly if it's a non-clinical thesis). This may not be the case across the board, but the few folks who had their MAs when they entered my program did not finish any earlier than those folks who didn't. We all also had to take the exact same courses.
A more tested route (if you are able to), is to finish your BA with good GPA. Get full-time RA work in a research lab (particularly in a research area you would like to continue), work for 2 years, then apply to labs/doctoral programs. If you can work some publications or posters into your RA work, and get high GRE scores, then you are golden.
Now as a 5th year clinical student, I'm really glad I took some time off of school to work, make some money, and have a good idea that I was making the right career move..