Best for what?
I mean, there are times I can only seem to be satisfied with a Lexicon 480 L ($8,000 back in the day)
Other times, perfectly happy with the mono Spring reverb in my ARP2600
...or anything in between.
Some old hardware units which have decent reverbs:
-Ibanez SDR-1000
-Yamaha SPX-1000
- Lexicon PCM-91 or PCM-81
At the end of the day, you need to know each unit's strengths and weaknesses before deciding what's best, and for which particular application.
D.