I prefer the Marathon. The difference is that the Blvd has a lot of extra padding on the sides. personally, I thought it made the seat a little too bulky and the Marathon still provided great protection. A lot of moms do feel more comfortable with the extra padding though.
i prefer the blvd because of the padding. it's a nice transition from ds at 6mos from his infant carrier. we took ds to bru and tried him in both and he just looked more secure and comfy in the blvd. i would rec doing the same, maybe it'll be different for your lol. gl.
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we have the diplomat (the smaller version of the blvd) and 2 marathons. i liked the diplomat for when the kiddos are smaller and the marathon when they're bigger. max is almost at the weight limit for the infant seat so i will be putting him in the diplomat and ryan in the marathon. when they're smaller the marathon does its job, but they don't seem so secure-especially just coming out of the infant seat.
Re: marathon vs. boulevard
BFP 3/9/12 Natural M/C 4/11/12