Hi R.,
With the exception of my (now almost 6) daughter's infant car seat, all we have ever owned are Britax car seats. I LOVE THEM!! I feel like my children are safe in them and that really gives me a sense of peace.
YES! They are big and they are heavier than others; they feel more solid to me. I wouldn't recommend getting any other type of carseat. Check out the features on the Boulevard vs. the Marathon. I think they may be the same thing and the only difference is the audible harness positioner. If you already know how to put your child in a carseat safely, I don't see why thing is needed... but when it comes to a child, you can never be too safe. Either choice would be great. Also, and VERY IMPORTANT, you MUST check and see if your car seat is AIRPLANE/FLIGHT APPROVED. I don't think the Britax seats are. I think you would regret lugging one with you unless you bought one of those little rollers that you can click the carseat onto and pull the child while they're in it. I believe I've seen them in the Right Start or Leaps & Bounds catalog/website. Still though, with the minimal amount of space one has in an airplane to move around, this seat would not be convenient either.
I am not sure the weight of your son, however, the 2 car seats you are looking into are 20-65 lbs. From 22-85 lbs. you can go with the Regent, which we have 2 of. It is still a 5 point harness and makes a nice booster seat for the later years. We did buy the 20-65 lbs. for our daughter before we bought the Regent. That way of doing things costs a lot of extra money when the difference between the 2 seats is only 2 pounds. The Regent is forward facing only and it does not recline, however, you only need to lean the seat back a little more in your car then. No big deal. Furthermore, if you like the head cushions in the Boulevard, there are pillows and things that can be bought separately on which your son can rest his head when he falls asleep. They are a lot easier to get the kids in and out of also.
The crotch strap has seemed short at times depending on what my kids have been wearing, but if you just loosen the shoulder straps a bit, there shouldn't be an issue. You tighten them back up nice and snug once everything is in place.
I hope this helps. Oh- if you have the OC Family magazine, there are up to $20 off coupons inside for Bergstroms Children's Store (located in Irvine or Anaheim). You would be able to use one of these toward any carseat if you wanted to go there instead of Toys or Babies R Us.
Happy searching!
Jennifer