personally id have to disagree with one or two points here about the challenger/abrams thing.The challenger is actually slightly worse than our current MBT, the M1A2 Abrams. It has weaker armour, is slower and about the same gun but less advanced targeting systems. The challenger is surviving because they are kept out of cities when ever possible. In a city a tank is extremely vulnerable, as witnessed in Iraq. The challenger is still an excellent tank though.
from what ive read on a lot of tank forums and seen on documentaries and the like the challenger is considered to have the advantage in terms of armour. Currently the main innovators in tank armour is GB with the armour the Abram is using being based on the British Chobham armour which we shared with the American Government.
the guns I do agree with, they are very very much on a par with each other but for different reasons.
the challenger currently makes use of a 120mm gun much like the American smoothbore gun but it happens to be rifled much like most small arms today. this tends to let the gun be more accurate in comparison to the American gun when un aided by tech. this gun also holds the world record for the furthest Tank Vs. Tank kill with an allmighty 5.1km kill. the rifled barrel allows the challenger to have more options in its shot type and allows the use of the favorite H.E.S.H rounds
the weapons do even out however when tech is included. The Abram is by far the most technically advanced tank out of the pair with a much more advanced and complex weapon system which allows greater group combat (sort of like that those radars you get in wing commander games.) the tech aiding the gun its self makes it more effective in the short-medium ranges than the challengers gun (but as most tank combat is about medium range so this kind of cancels out a bit).
the counter the Abram has to the tougher challenger however is very much faster and more manoeuvrable. this is thanks to its gas-turbine engines but sadly this bites back by limiting the tanks effective range due to consuming lots of fuel fast.
in brief id say that the tanks are very much on a par, with neither being better than the other. both geared for similar parts of the three feature balance of all tanks.
all tanks have followed this balance and every side has its own ideas on it.
but generally from what ive researched and feel personally id put things in this order
gun: draw (same calibre and generally the same accuracy)
so in conclusion, a draw in my own opinion