Yeah but the Britax's are known for their easy installations. The Scenera isn't that much more difficult than any other normal seat on the market. (In other words-you've been spoiled )

I love recommending this seat because it's CHEAP. There are a few, slightly more expensive seats which are also light which have higher weight limits.

This might interest you if you are planning on flying a lot. I had this contraption;
http://www.lillygold.com/

It's a great travel product but neither the best car seat nor best stroller. It's pricey too, for a seat which is usually outgrown at 2 1/2 approx. Because the top shoulder straps are very low, and children usually outgrow seats by height before weight, it's not the best value. My child used the Scerena 6 months longer and they both go to 40lbs.

Here is another seat. While it also has a 40lbs weight limit like the Scenera and the SitNStroll, it's very lightweight.

http://www.combi-intl.com/Products/Item.aspx?Item=12

Cute huh? It gets great reviews. It's light and easy to install. The price might be a factor. If I were having my first child, I think I would have skipped the infant seat and bought that, then used it for my next kids.

I now have a Radian. My dd is still in it at age 6 1/2. It fits basically all airplane seats and it folds. The only downside is the weight. It's about 25lbs but I put it on a luggage cart and it's good to go. I actually don't recommend that you buy one because your Marathon goes to about that age.

How to decide? The age of the child, how much air travel you plan to do, whether it's usually with one or both parents... But since you don't need the car seat where you're headed, I'll back the Scenera recommendations.

For the nitty-gritty on car seats, best to head over to Carseat.org for more information. You don't even have to register to ask on their forums and they're frequented by car seat techs, not just parents.