we have a Britax Roundabout 50. When we strap it in rf-ing, it wiggles too much and it feels unsafe. As a result we have had our kiddo forward facing for a few months (she is about 28 lbs.) since it sits very tightly flush with the back. Also we switch the seat out into gparents cars often (one has a captain's seat in a van, the other an suv) and we have found it still doesn't feel tight enough.
When I took it to the PD the officer that checked it said after 20lbs and a year to put her forward facing.
What's the best???