I have been to both (last year). Things may be very different now that they are the 'only game in town' for the most part.
I personally wouldn't ever go back to Blondie Spa. They've done some questionable practices (using fake pictures for their attendants for example) and the place was quite run down. I did have two of my best sessions ever at Blondie's but, that attendant is long gone.
Vaughn Spa is much nicer but the rooms are a bit small. I've also had some great sessions there but they had been getting into the bad habit of double-booking their attendants (I had to wait 20+ minutes in the room on two different occasions). That habit may even be worse now that the demand is up.
As I said, those experiences are from late last year and things may be quite different now.