The safest seat is the one that fits correctly in your car, you install correctly and you use properly every single time. All pass the same exact pass/fail testing to be on the market; seats that don't pass can't be sold.
That said, I would avoid the alpha omega. It's an okay harnessed seat but provides a deadly booster fit. The britax marathon is fine, but the shell is fairly short so kids outgrow it earlier than many other seats. I don't know much about the recaro, but I believe it's reputed to have less rear facing leg room than other seats (with the current recommendation to rear face to a bare minimum of 2 and longer if possible, preferably to 3 or 4, that's a big concern).
Seats I would look into (they're the ones I'm most familiar with, there are other good seats on the market as well):
Clek Foonf: very pricey, but the tallest shell and rear facing weight limits available. Also low profile, so it's not as bulky as many other seats, you can fit 3 across most cars and it sits lower on the seat. Will get even most very tall kids rear facing to at least 4, most likely you'll be able to rear face until the child moves to a belt positioning booster.
Diono Radian: Also low profile with a very tall shell and high harness slots and weight limits. This is what my kids ride/rode in and I'm very fond of it. It used to have issues with over reclining RF in certain cars, but they released an angle adjuster that fixed that issue.
Graco Size4me70: I believe some people are having issues with this seat, not sure if they're resolved, but it also has a tall shell and high weight limits. Bulkier seat as well.
Graco Myride65: Also bulky, but has high weight and height limits and a tall shell to allow for longer RF use.