I have a Record Doctor V and it does a good job. I recommend replacing the standard brush with a softer $8 goat hair brush - the standard plastic bristle brush can cause microscratches on records that are not audible, but can mar the appearance. The build quality is merely sufficient; I had to go inside my 3 year old RDV to reglue the downward suction tube recently.
Still, I purchased a Humminguru this year. I found that the time required to manually clean records on the RDV still left me with a pile of uncleaned records. The Humminguru is not really faster, but it is automated and I can do other things when the record is cleaning. Thus, I have cleaned a lot more records. I am also more apt to clean new records with the 'guru than I was with the RDV.
I still keep my RDV to clean really dirty thrift finds before putting them into the 'guru. I find that I am purchasing fewer of those recently and have been using the 'guru exclusively. The 'guru does clean records to a level that the RDV cannot do alone.