EDITOR'S OPINIONCompared to the Daleks, the Cybermen are interesting in that there hasn't really been one cohesive vision for them. Depending on who you ask and what story/era you're watching, they're either sadistic but sympathetic creatures that were once human, or they're vicious killing machines that downplay the human element.
I have to say I've always liked the late-60s, Second Doctor-era Cybermen. The combination of the uncanny prosthetics, the eerie voices, and the black-and-white visuals ensured that their presence was always eerie. Tomb of the Cybermen is in my mind, the definitive Cyberman story, and Peter Hawkins' vocal performance there is highly memorable. His "You will become like us..." line is famous as one of the most chilling cliffhangers the series has ever done. As well, he also provided the unnerving sing-song tone of voice the Cybermen had in their first appearance, which was abandoned quickly but nonetheless an effective performance. Roy Skelton's work was in the same vein, but without the aid of vocal effects. His robotic delivery but clearly human voice create a disturbing juxtaposition that reinforce the Cybermen as emotionless but once-organic beings.
Nicholas Briggs' performance is noteworthy as he voiced both the Lumic and the Mondasian Cybermen, which had different effects applied to them. The Mondasian Cybermen have deep, monstrous voices, while the Lumic Cybermen have high-pitched voices similar to the sing-song tones they had in The Tenth Planet. While the "Mondas" voice is more threatening, the "Lumic" voice does a better job of conveying their humanity.
In the end, Peter Hawkins and Roy Skelton are my favourites, followed by Nicholas Briggs, David de Keyser, and Peter Halliday.