Very similar to an earlier post, but:
Tier 1: Allen, Jackson, Mayfield.
I would not trade Allen for any of the other quarterbacks right now. But honestly, I would expect Browns fans to say the same about Mayfield and Ravens fans to say the same about Jackson. Based on their combined body of work last year and the first two games of this year, all three teams have to be pretty happy with their guy. Out of this tier, I am most optimistic about Allen and least optimistic about Jackson, but they're all in the same neighborhood and that is probably just homerism on my part. I was intrigued by Jackson pre-draft, and I'm happy to see him succeed. For those downplaying Jackson's 2-0 start because of the teams he's faced, I would remind of you of the glass-houses-thrown-stones axiom.
(small but noticeable dropoff)
Tier 2: Darnold
I like Darnold and expect that he'll get better. He had some good moments last year. But he didn't seem to improve much as the year went along (to be fair, I may have just missed it) and he seemed about the same in week 1. If I were a Jets fan, I would be at least a little worried my team drafted the next Ryan Tannehill -- not good enough to win games on his own, but just good enough that you can't move on from him. Then again, Eli Manning is the same kind of QB and he worked out well for the Giants.
(big dropoff)
Tier 3: Rosen
He hasn't even shown any flashes that I can recall, and the fact that Arizona watched him for a year and dumped him at the first opportunity says a lot. If Miami throws him into the starting lineup, he may literally get killed before the season ends.