Ultron-5

This series, alongisde "Next Avengers: Heroes of Tomorrow" has by the far the best written and cast Ultron to date. Tom Kane comes off as cold, eerie and completely logical on his Ultron, not to mention, he almost manages to beat the entire team by controlling the Mansion and knowing how to separate them properly, and his design is pretty cool too.

(Oh and the Mark I showing up for the final battle was also great, put a smile on my face as a kid and still did today.)