When you say greatest fielder - i'd assume all round natural ability to turn a .25 percent chance into a chance for a catch, runout or save runs in the field any wwhere and everywhere in the field.
My contenders would be
Eknath solkar - close in, Rahul would be pretty close but there was something freaky about Ekkie and the close in catches he took at silly point. Am not sure but possibly he is credited with giving Chandrashekar the nickname of 'Mill Reef' in honour of the horse that won the english derby when india was touring eng in the 70's, but he would hiss 'Cmon Chandra, reef it !' or cmon bowl the 'reefer' whenever he wanted chandra to bowl the quicker one

...Any ways i digress from the main topic
Slips - I'd go for Rahul - Safe, reliable, took most chances that came his way -so was Azhar who was a super slip fielder as well, kapil took some excellent catches, Sunny took max catches and rarely dropped any, but Rahul edges the others..
Covers, midwicket, 15 yard-30 yard circle - the contenders are Kaif, yuvi, Kapil, srikanth, Robin singh, Ravi jaddu, Azhar kohli and am sure am missing a few - Ghulam parkar was an excellent fielder in the 70's
Its very close between Jaddu, yuvi, kaif and Azhar...but for sheer num of times he has produced runouts out of nowhere-id go for Ravindra jadeja, a gun thrower , hit the stumps numerous occasions - and some unbelievable crazy cathces togo as welll
Outfield - contenders are Kapil - bullet like throw, he always chased & hauled in the
ball which looked boundary borne and rarely dived, and some terrific outfield catches, azhar in younger days also the same, but again Ravi jadeja has taken it to another level. He can sprint and make most 3's into doubtful twos even onthe boundary..and his throwing is diamond crazy bullet....
Overall, I'd go for Ravindra jadeja.....except i am not too sure about his slip catching or at gully - as those are pretty specific fielding positons but I am sure to a guy with natural hunting instincts like him - if placed there, he would make hgis presence felt and shine...