If the number of trains originating/terminating is considered, it is definitely a very important station. However, if the number of passengers are taken into account, NTSK comes ahead of DBRG.
Reason:
1> Tinsukia is surrounded by Arunachal Pradesh on 3 sides and serves as a hub for them along with its own population(also some towns of Dibrugarh like Naharkatiya, Duliajan, Namrup) and hence have better facilities like e-catering which is absent in DBRG which caters to the population of Dibrugarh only.
2>...
more... Recently 3 stations from Assam viz NTSK, Rangiya and GHY were selected for redevelopment. Again no DBRG.
3> Patronisation of 12085/86 and 12235/36 is lower compared to some other trains plying on the route as these trains skip NTSK and take DBRG-MRHT-SLGR route.
The other contender would have been LMG but after gauge conversion, it started losing its importance because people from south Assam and other adjoining states like Tripura, Manipur and Mizoram got a closer terminal in SCL and AGTL who earlier used to come to LMG to catch trains from DBRG.