I have the advocate and really like it. In case we are unfortunate to be in an accident, I want to know that I got my baby the best. It's easy to use and very comfortable too.
But I think you're comparing two great carseats.
We just had Erin from "Safety in Motion" come to our MOM's club meeting and do a car seat class - she is the instructor for HOAG and carseat expert for CHOC. http://www.safetyinmotion.org/ She loves Britax and told us she would get the Boulevard - but NOT the CS version. I guess she is seeing problems with them clicking before they are tight.
We got ours from diapers.com they are having a 15% off sale right now and you get it in 2 days!
BUT all the Britax's are really great.