Short version: Digiverb wins.
Long version:
I have never used a tank, so I can't comment on how close the pedal is to the tank. I find the Digiverb better in every way. The EQ control on the Digiverb works better than the Tone knob on the FRV-1 to warm things up, the Digiverb has more drip (actually, I'm surprised the FRV-1 didn't have more... sounded nothing like all the surf recordings.) I also hear a "digitalness" with the FRV-1 that I do NOT hear with the Digiverb.
I knew the Digiverb was more versatile (I still haven't found an equal to the "Church" setting), but I even prefer the spring setting on the Digiverb to the FRV-1.
So it goes back. Next up: the EHX Cathedral.