The MiG-25 Foxbat and the SR-71 Blackbird are two of the fastest aircraft ever built. The SR-71 was faster than the MiG-25. The MiG-25 had a top speed of Mach 2.83, while the SR-71 had a top speed of Mach 3.2. The SR-71 was also able to fly at higher altitudes than the MiG-25, reaching altitudes of up to 85,000 feet.
The MiG-25 was designed as an interceptor aircraft, while the SR-71 was designed as a reconnaissance aircraft. The MiG-25 was intended to intercept and shoot down high-flying bombers, while the SR-71 was intended to fly over enemy territory and gather intelligence. The MiG-25 was first flown in 1964, and it entered service with the Soviet Air Force in 1970. The SR-71 was first flown in 1964, and it entered service with the United States Air Force in 1966.
The MiG-25 was retired from service by the Soviet Air Force in 1994, while the SR-71 was retired from service by the United States Air Force in 1998.
Source: Rebecca Williams (Quora)