This
Amiga emulator is commonly accepted as the
best one available for
Windows.
It is commonly used with AIAB (Amiga in a Box), which means that all you need to emulate an amiga is a kickstart ROM and a copy of Workbench.
If you use Unix, you instead need to use UAE, but I have no direct experience of this, never having emulated an Amiga on a UNIX machine.