I forgot to reply about the seats we have... We had two marathons but one of the rear-facing piece broke on one of them when we switched cars in September, so we got the Graco Myride65, which I hate with a passion because the straps are a real PITA, but it was cheap. It rear faces to 40lbs supposedly (they'll have outgrown in length before that anyway).
Otherwise heard great things about Evenflo Triumph and the True Fit.
Whatever you do, the law now is that they have to be 20 lbs AND 1 year old to go forward facing... but yeah, recommendation is 2 (I think it's 3 or something in Europe now but their seats rear face longer from what I've heard). There are plenty of scary videos on youtube and articles you can google that will tell you why it's safer.