I picked the L-159. Here is why IMHO.
A proven airframe - but not necessarily a wimpy one. Will accept many different avionics for example.
http://www.airforce-technology.com/projects/l159/
COCKPIT
The cockpit arrangement and controls correspond to a modern fighter aircraft configuration. The Flight Visions Head-Up Display (HUD) with raster capability is the primary flight instrument and weapon aiming system. The multifunction colour displays are used for the display of flight and navigation information and weapons systems status. The Hands-On Throttle And Stick (HOTAS) control enables both pilots to control the aircraft without removing their hands from the throttle or the control stick.
The cockpit is protected with composite and ceramic ballistic armour. Survivability is also increased by the provision of a fuel tank inerting system, an On-Board Inert Gas-Generating System (OBIGGS). VS-2 zero ejection seats and a canopy jettisoning system are fitted. The standard aircraft configuration also includes an On-Board Oxygen-Generating System (OBOGS).
WEAPONS
"The ALCA has been developed in the single-seat L159A and two-seat L159B versions."The aircraft is equipped with a Hamilton Standards Stores Management System. There are seven hardpoints to carry stores: three under each wing and one under the centre fuselage. These are capable of carrying a wide range of NATO standard weapons, including AIM-9 Sidewinder air-to-air missiles, AGM-65 Maverick air-to ground missiles, rockets and free-fall bombs, a gun pod, laser-guided bombs, reconnaissance pods, electronic countermeasures pods and fuel drop tanks.
The system is adaptable for the future addition of new weapons, including medium-range air-to-air missiles and special pods for ECM, reconnaissance, night navigation and targeting.
COUNTERMEASURES
The electronic warfare system consists of the BAE Systems Sky Guardian 200 radar warning receiver and the Vinten Vicon 78 series 455 countermeasures dispensing system. Provision is made for the installation of an electronic countermeasures (jamming) pod.
AVIONICS
The avionics system meets multi-mission requirements and provides capabilities similar to current-generation frontline fighter and ground attack aircraft. Avionics integration is via a MIL-STD-1553 databus, which facilitates future growth. The avionics system performs the following functions: target sensing, controls and displays, stores management, communication, navigation and identification, self-protection, and data loading and recording.
The L159A aircraft is equipped with a Grifo-L multimode pulse Doppler radar produced by the Italian company, FIAR. For air-to-air search the radar has five modes of operation, can track up to eight targets and has track-while-scan capability. There are four submodes for air combat and nine modes for air-to-surface operations. The L159B is fitted with an electro-optical sensor or laser designator in the nose.
"The system is adaptable for the future addition of new weapons, including medium-range air-to-air missiles."The aircraft's autopilot and yaw damper, supplied by BAE Systems Flight Controls, has Stall Avoidance System mode (SAS), automatic attitude hold (ATT HLD), heading hold (HDG HLD), altitude hold (ALT HLD) and Control Stick Steering mode (CSS).
The Aircraft Monitoring System (AMOS) collects, processes and records data about the aircraft systems and aircraft loading, and provides automatic data retrieval and data transfer, via a Fairchild data transfer system, to the aircraft maintenance management system.
ENGINE
The aircraft is equipped with a Honeywell ITEC F 124-GA-100 engine developing a maximum thrust of 28kN. The F124 is a two-shaft non-afterburning turbofan engine with three-stage LP axial compressor. The HP compressor has four axial stages followed by one centrifugal. An Engine Monitoring System (EMS) is embedded in the dual Full Authority Digital Engine Control (FADEC) to store mechanical and performance data during flight, and has the capability to provide analytical and condition check-out on the ground.
Aero Vodochody is flight testing L-159 aircraft equipped with an in-flight refuelling probe.
In conclusion a very versatile choice, no matter what India picks for the 126 fighter tender