I'll go with the letter-grade system since this is stupid of me to post this anyway. Here's how I'd rank their albums from best to worst.
A In Rainbows - When I consider the greatness of the songs (particularly those on the bonus disc) coupled with a focus on Jonny Greenwood genius, I have to pick this as the best Radiohead album. That's also not to mention the wonderful album art. Unfortunately, it seemed like people spent more time talking about how they released it instead of how incredibly they layered the sounds.
A The Bends - Mostly for nostalgic reasons, this is my favorite Radiohead album. At times, the quality of the songs seemed compromised (probably due to the pressure of following up Pablo Honey), and I can't help but wonder how much better the album would be if it had been released more recently. But at the same time, I think it featured their best pop moments as if to say, "We've grown up quite a bit since Pablo Honey."
A OK Computer - This is understandably the favorite album of many Radiohead fans, but I would say it's possibly the most overrated. To be clear, that's not meant as a knock--t's an excellent album all the way through--but I feel like some of the ideas should've been developed more. Still, it's considered one of the most important releases of all-time for good reason.
A Kid A - This album features some of Radiohead's best moments (I don't know many artists that can top "Idioteque"), and I admire how groundbreaking it was. On the other hand, it didn't "capture" me in as many ways as some of their other stuff.
A Hail to the Thief - I wasn't immediately enamored with this record, but it kept growing on me the more I listened to it. Maybe I'll like it less/more in the future, but at the moment, I feel like it's up there with their best (although I skip a couple tracks on most listens).
A- The King of Limbs - It blows my mind that there are people out there who liked their previous albums but didn't like this one. I'd recommend that those people give it another listen because they were probably just disappointed with the direction they went. Musically, it struck me as their most collaborative effort and shifted the focus away with Thom Yorke. That might not seem like a good thing, but I thought they sounded more natural and helped enable the songs to flow well from one to the next.
B Amnesiac - This is my least favorite of theirs. I've heard it called "Kid B", and as much as I loved Kid A, it just seemed like a not-quite-as-good version of it. I'm probably a little harsher on this record than I should be, but I fell in love with their ability to change their sound, and they didn't do that here as much as I would have liked.
C+ Pablo Honey - It's a good album that I used to hate but have come around to respect. When I was younger, I didn't "get" music like I do today, but now that I've grown up a bit, I still have to admit there are some boring moments. I certainly didn't expect them to improve as much as they did, but in hindsight, I shouldn't have been so surprised because there were definitely some incredible moments.