I'd look at the TrueFit and also the Complete Air. The Complete Air RF to 40lbs instead of 35, and FF to 50lb instead of 65lb, but it is a similar height so will last most kids to booster age like the TrueFit. The TrueFit is almost never outgrown RF by height (it is very tall). Some folks on here get pretty amazing deals on Radians (like under $200) if it works in your vehicle. Also, some places will give you a twin discount if you buy two.
So, for tall kids, big cars and a long-lasting seat, I'd look at the Radian, the Complete Air, and the TrueFit, pretty much in that order.
I wouldn't consider Britaxes at this point, they don't make any convertibles that are really great right now, iMO.
As far as spending the money, you are going to need a convertible anyhow - kids just outgrowing a bucket seat shouldn't be FF yet - so even if it doesn't work for you now, you'll need it soon enough.
From your siggy, they are 9 months old? At that age I suspect they'd like the convertibles, and I'd install them fairly upright (up to 30 degrees for the Radian or Complete Air, up to 35 degrees for the TrueFit). My DD was a screamer, she got much better around 12 months, and actually started liking the car by 18months.
: mamas to one DD (5/08) and two DS's (11/9/10 @ 35wks)