What we call the world's highest performing aircraft depends on what category of performance we are looking at: size, speed, or stealth. All of these qualities may be the most useful depending on application.
The world's largest passenger aircraft is the Airbus A380, which can carry up to 853 people in economy class configuration. The Airbus is so huge that the nickname "Superjumbo" was made for it, and it can only land in specially-designed airports. So far, the vehicle has only flown for test and show flights, but it is ready to enter service in late 2007 or early 2008.
There are several extremely fast aircraft. Which you call the fastest depends on your definition of "aircraft," but generally an aircraft must 1) be able to take off unassisted, 2) work in the lower atmosphere, and 3) land unassisted. The fastest craft, scramjets that operate high in the atmosphere, do not meet this definition, however they can be extremely fast. The fastest scramjet yet flown is the Boeing X-43A, which set a speed record of 7,546 mph (12,144 km/h), or Mach 9.8, on 16 November 2004. The fastest true aircraft is the SR-71 Blackbird, which reached a speed of 2,188 mph (3,521 km/h), or Mach 2.8, on 28 July 1976. Various rockets have reached speeds in the Mach 5-7 range, but these cannot take off or land on their own. The fastest aircraft is technically the Space Shuttle, but again, it cannot take off on its own, and achieves its top speeds out of the earth's atmosphere.
The title of world's stealthiest aircraft is a toss-up between the F-22 Raptor and the B-2 Spirit bomber. One could argue that the F-22 Raptor is stealthier because it is smaller and therefore probably harder to detect. Both are extremely advanced and expensive aircraft used by the United States military. They do not appear on radar, but must be spotted visually. The Joint Strike Fighter, currently under development by the US and UK, will also be a highly stealthy craft, and its updated design will probably make it even harder to detect than either the F-22 Raptor or the B-2 Spirit.