Hi S.,
The top-rated car seats according to the Consumer Reports website are (in order):
Britax Diplomat $260
Cosco Scenera $60
Graco Comfort Sport $90
Maxi-Cosi Priori $200
We have a different Britax, and I think it's the most comfortable car seat we have. We bought three: one for my car, one for my sitter's car, and one for my husband's car. I bought the two highest rated seats at the time, which were the Britax Marathon and the Triumph Advance. The Triumph is huge, which is why it ended up in the sitter's minivan. I also bought a $64 Cosco seat from Target for my husband's truck. It's fine, but the seating is a bit firm and I don't think it's as comfortable as the Britax.
If you have a Britax, I think you should stay with that brand. One of their models usually ends up being the top-rated one on Consumer Reports.