Best Amiga Today???

[Lando]

Real Amiga (w/add-ons & extras, but must start w/Amiga MoBo)

A4000 + CSPPC 604e-233Mhz / 060-66Mhz / UWSCSI, PCI busboard (Mediator, G-Rex or Prometheus), Voodoo 3 graphics card, DKB3128 RAM board, Video Toaster 4000, and whatever else you can cram in there.

Emulated/Imitated Amiga (list emulator or clone OS and hardware)

Toss-up between Pegasos II + MorphOS and WinUAE.  

Pegasos II G4 beats an Athlon 2800+ overall according to the AmiGOD benchmarks page and has the added benefit of running WarpOS and PowerUP applications and a number of OS4 applications (via OS4Emu) which the PC won't so I'd have to go with that.

Most compatible with all existing software (will run most programs)

A500 1.3 or PC with WinUAE.

Fastest Amiga (Emulated or Accellerated?)

A 3Ghz+ PC with Amithlon or UAE.

The Ultimate Amiga (which of the above is best)

Depends what you want to do with it.
Best bang-for-buck has to be the PC with WinUAE.

[Lando]

WInUAE the most compatible Amiga Option for classic Amiga System,
run any software for any kickstart or hardware up to Amiga4000,
whit the limiton of not being able to run PPC software

That's where the advantages of MorphOS come in.  You can run WarpOS + Warp3D apps, PowerUP applications, 68k applications, native MorphOS apps, native OS4 apps (through OS4emu) and hardware-banging 68k games (through UAE) all at the same time each in it's own window, and still faster than the real Amiga.  

The only system that can do this.