Saracens centre Barritt shone in England's midfield as his hard-hitting defence set the tone for England to win four out of their five matches.
Brown's Championship was limited to three replacement appearances against Scotland, Wales and Ireland but his performances at full-back for Harlequins have been a major factor in the London side topping the Premiership table.
Leicester flanker Julian Salvi, Gloucester prop Nick Wood and Exeter Chiefs flanker James Scaysbrook make up the final three contenders.
The 25-year-old Robshaw won the award back in 2009 and his case for a second accolade could be strengthened if Harlequins finish top of the pile with a win over Sale next weekend.
The winner will be announced on May 8th, four days prior to the Premiership semi-finals.