A T-rex would be about 7 tons, 18 feet high and 40 ft long. Dr. Robert Horner showed the lower leg fossil of a T-rex and place where the ligaments and tendons attach was huge, suggesting a top speed of 45-50 MPH. A M1 A1 tank does 45 tops. Due to the T-rex's huge tail being a counter balance to the huge head, the T-rex probably has the agility of a squirrel-meaning it would seriously out-manuever any tank, any day.
T_Rex would hands down win.