Like the two posters above, I've seen loads of other people say that Duelling Dragons is the best themed queue in the world (or words to that effect), but I'm going to be a little controversial here and people probably aren't going to like it

, but I think it is very poorly designed!
My main gripe about it is if you go on a day when there's not many crowds (as I tend to), you still have to walk through the entire castle, which assuming you don't get lost takes about ten minutes - there is no way to cut out sections of it like the queues on most other rides are set up.
And that note above about not getting lost - yes you CAN!

Once I was behind a couple going through the queue but not really paying any attention to where I was going apart from following them (they had no-one in front of them). Suddenly I realised we'd passed the same bit twice - in the dark, they'd taken a wrong turn and walked down what I can only presume was a chicken exit or a staff tunnel and ended up coming back out about 200 yards further up the queue and had to do it all again! Because the queue is so dark, I think quite a few people probably do this and don't notice.
The final bit I don't like about it is the bit where you choose between Fire and Ice. Having spent all that time walking through the queue, the bit where it tells you to pick with the video of the wizard is about ten yards long. And so most people I've seen don't even realise there is a choice at this point and just follow all the people in front of them onto the same side of the ride. If they are going to make you walk all that way, at least they could split the queue a little earlier and clearer so people who've never been on the ride before realise what's going on. All the other rides in the park with a choice (like Hulk's front row) are clearly marked long before you reach the point, but not DD.
That's my moan over. Just had to get that off my chest!
My choices for best queue are Spiderman (like walking through the Daily Bugle office, plus the video at the loading area is very funny) and Revenge of The Mummy (but watch out for mischevious cast members trying to scare you!)