I prefer the classics. Profondo Rosso (Deep Red), Suspiria, Tenebrae and Phenomena. The 90'ies and 2000's sucked as far as his films are concerned (compared to earlier works). The only "modern" Argento movie I liked was No Ho Sonno (Sleepless) with an amazing intro theme track by Claudio Simonetti and a somewhat tired Max von Sydow.
Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn!
"The sky was the color of a TV tuned to a dead station" - Neuromancer