06551 is best because of new LHB rakes, but it will discontinue as the rakes belongs to 22685/6 YPR - PUNE - NZM - CDG biweekly exp, and it has to start. Where as 06511 is having idle rakes of GR and it is long running GR, record braking performance for 3 consecutive year, most reliable/punctual spl train, cleanliness at it best.
We can consider 06529/30 as good contender with 21 coaches idle rakes, and can be made permanent, in coming budget.