The British Challenger 3 tank and the Russian T-14 "Armata" are two fundamentally different approaches to armored vehicle design. However, the development by Rheinmetall BAE Systems Land has the advantage, according to military expert Steve Balestrieri in an article for 19fortyfive.
The main problem with the previous generation Challenger 2 tank was the L30A1 rifled gun. The solution was to adopt the 120 mm L55A1 smoothbore gun from Rheinmetall.
The T-14 "Armata" is a microcosm of the Russian army. Hyped but problematic, its production has practically ceased. The tank has not been used in combat.
In 2021, Rheinmetall received an order from the UK Ministry of Defence to modernize 148 Challenger 3 main battle tanks. This involved improving the turret, armor, active protection system, and targeting system of the armored vehicles.
The T-14 "Armata" boasted a number of technological innovations that, on paper, indicated the tank's superiority. Unlike the Challenger 3, the T-14 has an unmanned turret, reducing the crew to three people. Its 125mm smoothbore gun fires both conventional ammunition and anti-tank guided missiles.
According to the author, the T-14 is "technologically ambitious and theoretically very impressive." The tank received the "Afganit" active protection system.
Russia probably has 50 T-14 tanks. Why don't Russian commanders like to use it in combat? Knowing this, I would give preference to the British Challenger 3.
Read more on the topic:
The National Interest: Russia Fears Losing Its "Too Valuable" T-14 "Armata" Tank
T-90 and T-14 "Armata" Included in the Top Ten Tanks in the World