We have narrowed it down to the Marathon and Boulevard. I am torn between the two and trying to decide if the Boulevard is worth the extra money, or if it's overkill. The main reason I'm considering it is b/c I drive a 2003 Tahoe and do not have side airbags in the backseat. Then again, it's an SUV, not a small car.
Anyone choose Boulevard over Marathon? If so, are you happy with your choice and do you feel it was worth it?

Re: Anyone choose Britax Boulevard over Marathon?
According to the measurements listed on Amazon, the Blvd is only half an inch wider. Did you have any issues fitting two side by side?
Ditto including not remembering why we chose them. :-) They have been great and DDs seem very comfortable in them. We have a minivan and have them in the 2nd row captain's chairs so no clue how they would work in a bench seat. We got ours from albeebaby.com
***Twin fraternal girls born at 35w6d in 12/2008***
I picked the Boulevards too. I took the kids with me to BBB when I was looking at them and I put DD in a Marathon and then in a Boulevard and seeing her tiny head in between the padding versus just bobbling free and I was sold. Sure, it might be overkill. But it makes me feel better and the price difference wasn't so drastic that I thought it was worth it.
We got one at BBB with a 20% off coupon and had enough store credit from registry returns to pay for the difference. The other I bought through Albee Baby with their 25% off sale.
Ditto exactly what keg said above.
I think I saw a comparison chart of the different Britax seats and Boulevard stood out to me...but I don't remember where I saw it. This post is proof that kids zap brain cells! ;-)