Well have come across an excellent old article on comparison between ARJUN and t90s tank posting it here so that people can specifically debate on details.
General Characteristics of MBT Arjun and T-90S
Battle tank design is an optimization of the three basic characteristics viz. firepower, mobility and protection. All tanks are designed in accordance with the war doctrine of the country and to ensure operation over a range of environmental conditions. Arjun MBT is a state of art tank, developed to suite specific needs of Indian Army. Arjun MBT is on par with contemporary tanks in its class like M1 Abrams, Leopard 2, Leclerc and Challenger II. T-90S is a lighter tank and does not fall in the class of Arjun MBT. T-90S is designed in accordance to specifications of the Russian Army and Russian cold climate. Both Arjun MBT and T-90S can be transported to Indian border areas by rail throughout the National Broad Gauge network.
Arjun MBT's Hydro Pneumatic Suspension system provides a stable weapon platform which enhances the fire on move capability and excellent riding comfort during cross country move. The Indian borders in north and west are very rugged. Arjun MBT has less Nominal Ground Pressure (NGP) compared to T-90S. Arjun MBT has better acceleration and maximum road speed due to high peak torque output of the engine coupled with fully automatic transmission not withstanding "slightly" lower power to weight ratio. Automatic transmission provides neutral turn capability which adds to the maneuverability during shoot and scoot. Arjun MBT features Auxiliary Power Units (APU) which T-90S does not have. APU's provide continuous operation in silent watch mode. It also saves main engine life. Rubberized double pin tracks provide increased life, reduced track noise and better maintainability. Arjun MBT's mission reliability has been proved with 500 kms being covered in 48 hours. Arjun MBT successfully crossed the RAVI River at Lassian without support systems due to lower ground pressure. Trench crossing capability of Arjun MBT is on par with T-90S as Arjun MBT has seven bogie stations compared to six bogie stations of T-90S.
Firing performance of Arjun MBT is superior to T-90S in terms of accuracy (both static and dynamic situations) due to gun ammunition combination and high order of weapon stabilization coupled with auto collimated MRS. Auto collimated MRS compensates for the barrel bend. Firing performance of Arjun MBT and T-90S is same in terms of defeat capability and rate of firing. Two axis stabilized commander's panoramic sight integrated with gunners main sight provides "hunter killer" capability both in static as dynamic mode (moving to moving mode). Higher order of stabilization accuracy enables accurate fire on the move at a moving target while maintaining the stipulated fire rate. The commander of Arjun MBT can engage targets in case of emergency, capable of firing at various slopes and tilt angles. First round hits probability has been demonstrated for MBT Arjun on a 1 mil target and greater than 60% hit percentage when firing from a moving Arjun tank to a moving target, both at 25 km/h.
LAHAT (semi automatic homing) Missile firing from Arjun MBT has been already demonstrated using a stand alone Laser Target Designator (LTD). This designator can be integrated into Gunner's Main Sight (GMS). T-90S can fire Laser bean riding missile..
Arjun MBT armament system including gun barrel has been proved to be robust and reliable No case of barrel burst was reported even after firing 10000 rounds. The Arjun MBT prototypes and pre production tanks fired more than 100 rounds from the same barrel in a day. Life of barrel of Arjun MBT is twice that of T-90S, estimate equivalent in Effective Full Charge (EFC) of 500.
Protection of MBT Arjun against FSAPDS and HESH ammunitions has been demonstrated. In January 2000 at Proof & Experimental Establishment (PXE), Balasore, Arjun tank armor defeated all available HESH and FSAPDS rounds including Israeli FSAPDS rounds. ERA is effective only against HEAT ammunition and not FSAPDS which is the primary threat to a battle tank. Arjun Tank has ERA protection as add on feature, while T-90S has it as a regular feature. A tank with ERA has a weight penalty.
Outcome
Indian Army has not expressed the purpose of this exercise. It can be various reasons like a genuine requirement of validating its GSQR which resulted in creation of a heavy tank or the Indian Army internal rivalry or the pressure from the import lobby to kill the indigenous Arjun MBT project. It will be the test of Indian Army's own integrity as Arjun MBT was made as per the Indian Army General Staff Qualitative Requirement (GSQR), tested by Indian Army and approved for production by Indian Army.