Ur statement is full of biasness.
It's already stated that the Type 99 has the fastest speed. How is Russia being the 'most agile' when it's the slowest out of the 3. Or is it because the Arjun is an export variant of the Russian T-90 that makes u think it's the 'most agile'. Define what is 'most advanced'- advanced in what? M1 has a 120mm gun- the Type 99 has a 125mm one- yet according to you, M1 has the most firepower.
Agile means 'characterized by quickness, lightness, and ease of movement; nimble'. The Russian T-90 could have the lowest top road speed while still being having the best speed in the field, or turn rate, or accelleration, or a combination thereof, which one could call 'agility'. When comparing Leo2, M1 Abrams and Challenger I/II, the latter is often said to be the best off-road, while the Abrams and Leo2 are clearly faster on roads.
Don't attack someone on the Arjun when that person hasn't even mentioned it in its post. That is just lame.
Advanced means 'at a high level of development' absolutely (i.e. at the forefront of development or technology) or relatively (ahead of others in the same field). If you say 'advanced tank' that refers to all aspects (firepower, mobility, protection, C4I).
When comparing the relative merits of the US/German 120mm smoothbore and the Russian or Chinese 125mm, it is not the caliber that matters but barrel length and the nature of the round. So long as the Russians or Chinese use an autoloader and two-piece ammunition, the one-piece 120mm round (with a longer, heavier penetrator) will have the advantage.
All the Russian 125mm's from 2A26 through 2A46M have a barrel length of 6000mm. So, they are 125mm L48. Ukraine makes these as KBA-1, KBA-3 and KBA3K 125 mm tank guns.
http://fofanov.armor.kiev.ua/Tanks/ARM/2a46.html
http://www.morozovkmdb.com/eng/body/kba3.php
http://www.morozovkmdb.com/eng/body/kbm1m.php
Ukraine offers a 120mm smoothbore for upgrading Russian tanks, with a bustle mounted autoloader. It is called KBA-2 and also has a barrel length of 6000mm (L50)
http://www.morozovkmdb.com/eng/body/kbm2.php
The US M256 gun is essentially the Rheinmtall 120mm L44. As the standard NATO smoothbore gun for main battle tanks Leopard 2 and AbramsM1A1, Rheinmetall’s L44 tank gun proved superior to all rivals in the 120 mm arena. The German Rheinmetall 120mm barrel on Leo2 originally was L44 (5280mm) but in newer versions is replaced by an L55 barrel (6600m). A difference of 1320mm. In the L 55, a larger share of the energy resulting from a round being fired is converted into greater velocity. This leads to an enormous increase in maximum range.
http://www.rheinmetall-defence.com/...mmunition/direct_fire/large_calibre/index.php
The main armament of the T-14 Armata is the 2A82-1M 125 mm smoothbore cannon, a replacement for the 2A46. The 2A82-M1 is undoubtly much more powerful than any previous 125mm gun, it uses a full new technology and larger chamber for a new pattern of semi combustible propellant case. It's said to be 15-20% superior to the recognized king, the 120 L55. 2A46-M5 is the best and latest iteration of the 2A46, it equips T-90A, T-72B3 and some T-80U. This gun is already
approaching L55 120mm performance, and outclass the L44 by a good margin, it's comparable to the French 120mmL52.
Rheinmetall Weapon and Munition has unveiled a new 130 mm smoothbore tank gun at Eurosatory 2016 in Paris. The new 130 mm smoothbore gun is an L/51 weapon (6630mm).
http://www.janes.com/article/61255/eurosatory-2016-rheinmetall-lifts-the-lid-on-new-130-mm-tank-gun
The new 130 mm gun is a precondition for the future tank, known as ‘Main Ground Combat System’ (MGCS) being developed by Germany. MGCS is currently being developed by Germany and France as a future replacement for the Leopard 2 and Leclerc main battle tanks, in response to T-14 Armata.
http://defense-update.com/20160614_rheinmetall-ups-tank-firepower-with-new-130mm-gun.html
Both Leo 2 and Abrams in the past have trialled with 140mm cannon...
Swiss
German
with XM291
Abrams CATTB (Component Advanced Technology Testbed).