For plain ol' amp spring reverb, I like the EHX Holy Grail Plus the best.
For the Fender '63 Reverb Tank surf-type reverb, I think the Verbzilla & Digiverb do this best. Out of the 2, I prefer the Digiverb. I just sold my Verbzilla & kept the Digiverb.
The Holy Grail is transparent. (and just to be clear: get the Holy Grail PLUS, not the old HG).
The Digiverb sucks a LITTLE tone, but I run a dedicated buffer on my board anyway, so it's not noticeable. And I'm anal about that stuff.