1. Michael Wisher
Wisher is to Davros what Delgado is to the Master. Davros in his original appearance is fascinating because he's utterly convinced that he's the hero of his own story. However horrifying his ideas and actions become, his motivation never strays beyond the comprehensible. Even at his most barbaric, he comes across not as a stereotypical mad scientist, but as an extremely intelligent man with a robust survival instinct responding in what seems like the only rational way to the impossible situation he's been living with for the better part of a century. A solemn, serious-minded man of immense passion and conviction whose moral compass has become so skewed that he regards genocide on an unprecedented scale as a noble and virtuous route to peace. Wisher may have had the advantage of starring in arguably the greatest serial in the show's history, but his chilling, understated performance plays a crucial role in selling the character.
2. Terry Molloy
A close second. Molloy was the Davros of my childhood, and I'll always retain a certain nostalgic fondness for him. As an actor, he's definitely a worthy successor to Wisher. My only issue is that (as much as I enjoy them both) Revelation & Remembrance pushed him a little too far in the cartoon villain direction - which he pulls off brilliantly, and is only really a problem when compared to his characterisation in Genesis. His stunning work for Big Finish more than makes up for it. I've often wondered why he wasn't invited back for NuWho, but that turned out to be a blessing. Speaking of which...
3. Julian Bleach
Bleach is an excellent actor and an inspired choice for the role. Unsurprisingly given RTD's previous work, the Series 4 portrayal was too deranged and overemotional, with the cackling, screaming, etc. somewhat lacking the cold, considered, scientific edge that initially made him so compelling. Still, a first-class performance. As for Series 9, he did as well as anyone could with the abysmal material he was expected to work with, but the character was humiliatingly desecrated, one of many to fall victim to Moffat's egotistical rampage of postmodern revisionism.
4. David Gooderson
Meh. Do I really need to justify this one? The bit where he slaps away Tom's bag of jelly babies is priceless, but that's about all he has going for him. A textbook miscast, if you ask me.