I'm having a store-bought bagel (Thomas's, of English Muffin fame) as I type this.
TOD
I think onion bagels were my first favorite back in the day, and I've been through several phases of favorites. [Onion sandwich rolls were also a staple back then, I just remembered.] Nowadays, I ALWAYS like an everything bagel. For a basic one, sesame seed is my cherce. I think I'd consider a salt bagel as the most exotic, since it's so outrageous from the get-go -- but SO good, just once in a while, toasted with butter. Oh yeah baby. I'm afraid I find plain bagels boring, and poppy seeds themselves don't do much for me except leave black dots on my teeth.
Though I've had many over the years, I no longer find myself interested in blueberry or whole-grain or other bagels of that stripe. All of those ingredients, IMHO, are better served in regular bread products other than bagels. I don't see the point. Bagels are just a little too unique or individual a thing to have been given such a "mainstream" treatment, even though of course it's inevitable that it happened. And I don't mind -- I'm glad bagels themselves became infinitely more available over the years. Just keep my everythings coming, along with BK's onion, and everybody will be happy.
Best bagels? The New York dense but chewy, hands down. Even there, there's plenty of variety. I've had some from Arthur Avenue in the Bronx that I thought were among the very best. I liked H&H (are they still around?). The single best bagel experience that stands out in my mind, however, was a day that some friends and I met in Manhattan to go see some museum exhibit out in the wilds of Long Island. We had to stop in Great Neck to pick up the last person, and they knew a convenient bagel place to meet. That jernt was the most bustling and amazing one I've ever been in, and everything there was to die for. For years I've meant to find it and go back for a bag of bagels.