>Most compatible with all existing software (will run most programs)
AmigaForever(WinUAE)
I do not think so. For example WinUAE will not run any software that make use of Amiga Zorro cards such as Movieshop.
What can UAE can do that a real Amiga can not do ?
As for speed it would definitaly be a peg2 G4 (fast JIT + native OS and software). However some 68k software may run faster emulated on an extremely fast PC.