Well, clearly the problem is there were three people driving!
Since there is no perfect seat . . .
What do you like about the TrueFit? What do you like about the Marathon? Any other seats you've owned?
I liked the way that she fit in the TF. I liked how it installed. I liked the way the MA in stalled as well. I also liked the not twisty straps on the MA and the non continuous staraps.
What don't you like about all of the above seats?
I do not want another MA. I do not like the recent test results for it. I don't like the continuous harness or the twisty tongs of the TF.
How much growing room does she have in the TF? According to your siggy, she's FFing in the Marathon. Are you interested in maxing out RFing? What do you like about the idea of the Radian? At 4 years old and part-time forward facing, have you considered getting a combination seat instead of another convertible?
RF she is right above the 3rd slots. I would like her to RF, but have no problem with her being FF. I like the Radian because of the low sides on the bottom. It would give her more leg room options. I really like the head wings as well. The only FF combination that I like is the Nautilus Elite (the lock off).