Cinnamon raisin is slightly better than blueberry to me (plain is third). French toast bagels are rather good as well when used in a bacon, egg & cheese sandwich.
Cheese bagels reign supreme, but cinnamon raisin is a close second. Onion is also quite good. I like blueberry as well, but prefer it with a strawberry or mixed berry flavored cream cheese.
I actually didn't know half them flavours of bagel existed before this thread so I'll stick with the tried and tested plain flavour that has never let me down.
If they make bagels like the Parmesan oregano bread from Subway then I'd have to rank that number one, but I've never seen any.