J.O.
The safest will be a rear-facing seat until the child is at least 2 (but ideally 3 or 4). Britax are fine as all seats pass the same safety testing. So you just find what you like, and what fits your car and child.
If you choose a Diono brand you can easily rear-face most kids until 4, which would be the safest bet due to the length of rear-facing. But do see what works with your car. The Dionos are narrow, which is a nice feature if you need that. Can even do 3 across!