The Yank Tank. Named for General Creighton W. Abrams.
Enthusiastic and blindly patriotic Americans will tell you that this is the best tank in the world. It is so good that its mere appearance on the battlefield will scare T-72s into spontaneously exploding and popping their turrets in catestrophic kills. No other tank can match it. Etc, etc. So taken in are many by their own propoganda that they couldn't understand how it was possible that some Iraqi bloke with an RPG-7 was able to put a hole in the side of an Abrams. It was theorised that some super-advanced Russian ATGM was smuggled into the country, AT-14 being the common suspect. It is now accepted that perhaps the Americans were over-estimating the tank.
That said, in its latest incarnation, M1A2SEP, there probably is no other tank which is as good as it in its designed role: The destruction of armoured hordes on the battlefields of Europe. The problem occurs in the fact that this is no longer the de facto role of tanks.
Versions: M1: The original prototype and production version. After the expensive failures of the MBT-70 and Austere tanks, the US Army was getting antsy for a new tank which (a) worked, and (b) was cheap. OK. The Army didn't care about the cheap bit, but congress did. As a result, a competition was held, General Dynamics/Chrysler won the bid, and away they went. The turbine was not entirely revolutionary, the Strv-103 had one, but was certainly still novel. It made the tank very quiet, and has huge torque with few moving parts. Whilst it was always intended to have a 120mm or better gun, and separate sights for commander and gunner (The mounting point for the commander's sight being the round protrusion in front of the loader's hatch), the desire to keep the tank cheap meant that they would ditch the sight entirely, and used the British 105mm cannon of which they already had ammunition and parts for since it was also used in the M60 series and M48A5 tanks. Of course, cheap is a relative term. In the early 1980s, you could drive away an initial series M1 tank off the showroom floor for one million dollars, plus tax, registration and options. Coax and loader's MGs were M240s, TC had a .50 cal. Visibly identified by the lack of a bustle rack.
M1IP: Improved Product M1. Same 105mm cannon, but addition of a bustle rack, and more armour.
M1A1: First showed up around 1984. The Army finally got the money they wanted to put a bigger gun on the tank, using the German smoothbore. Otherwise, pretty similar to M1IP. ($2.4 million)
M1A1HA: Heavy Armour. (Also known as the Common Tank, because the US Marines uses it). Added inserts of depleted uranium to increase defensive capability. Boiling vessel added, located in front of the loader.
M1A2: The digital tank. Changes are the removal of the .50 cal's x3 remote control system, and replacement with a flex mounting to increase visibility. Addition of commander's independent thermal viewer for hunter/killer capability. Addition of battlefield command system. And lots of electronic doodads inside. Air Conditioning added, though it's more for the computers than the people.
M1A2SEP: Latest and most expensive tank. ($4.2 million). Amongst the improvements are the replacement of the x10 thermal imagers with x50 FLIRs, finally allowing the crew the ability to see what the devil it is they're shooting at. Up until then, target ID at longer (2500m+ ranges) was impossible. They'd just see a hot blob.
TUSK: Tank Urban Survivability Kit. Recent experience in a certain middle-eastern country which shall remain un-named showed deficiencies in the design in that sort of combat. This upgrade consists of ERA blocks on the sides, slat armour on the rear, gunshields for the loader, remote .50 cal for the TC, a telephone, and a few other things.
Turbine: Texas-Lycoming 1,500 hp, does about 4 gallons to the mile and drains the 503 gallons of fuel leaving a sizeable hole in your wallet when you pull in for a fill-up. Exhaust makes a wonderful heater. Also useful for dispersing crowds.
Ammo: MPAT, HEAT, Sabot, HE-OR, Cannister.