Now, this is a really easy one. No contest.
The big squid-thing has to be one of the most awesome villains in the history of villainy. Such a fascinating character. So vitally important to the story– look how it changed the entire history of Middle-Earth by giving Frodo a scare and eating up Óin or Glóin or Sleepy or Happy or Grumpy or whoever it was. Not to mention the fact that it would probably make
great calamari.
Why Tolkien had to go and name the book after some sissy jeweller when he could have called it
The Watcher in the Water or
The Thing With Lots of Tentacles or simply
Squid! I'll never understand. I'm sure H.P. Lovecraft would be with me on this one.
Nevertheless, for some reason I feel compelled to vote
++Sauron.