Do you have a favorite comic book robot? It has to be a robot, or at least a cyborg, and not just a guy in a suit of armor.

I think I will go with Ultron. He is one of the most evil robots ever, and quite a powerful foe. His many variations of the years have been quite interesting. I especially liked the bizarre "Acts of Vengence" story where he showed up in Daredevil. Ann Nocenti sure did some strange things with that book.

Here's my picks:

Robotman (DC)
Big Guy & Rusty (Dark Horse)
Robot (from Image's Invincible)
Vision (Marvel)
Red Ronin (Marvel)
Red Tornado (DC)
Machine Man (Marvel)
Braniac (DC)
Amazo (DC)
Metal Men (DC)
Amazing Screw On Head (Dark Horse)
all those Spider-slayers (Marvel)
Doombots (Marvel)
and lastly,
those 'bots that Magnus was always karate chopping to pieces.

Red Tornado and Braniac

Red Tornado here too - great character design and most writers, particularly with the JLA in the 80s were able to nail his attempts to understand humanity - his loss in the first crisis really hit me at the time.

currently reading the trades of 52, so i gotta throw Skeets in here too.

Dethlok

I used to enjoy "Scud-The Disposable Assassin"

Braniac for me. I honestly can't come up with a second place either, not because I love Braniac, but because I can't think of another one that I really like.