With some special definition of "comparable". ;-)
(Maybe what he *really* meant to say was "not particularly comparable at all"...

)
Well, to sum things up:
If you are mostly interested in Retro stuff, and want to use the good old Amiga SW without any compromises whatsoever, then there are two options:
1 – If Amiga HW is part of your Amiga interest, then you want a real Amiga, and the A1200 + accelerator option as Crumb mentioned above is a good option.
2 – If you are mainly interested in using the Amiga SW, but on a machine you already have (probably x86), then UAE (WinUAE) is a very good option. The "Amiga Forever" from Cloanto is a complete package, with many extras.
If you are more interested in using the Amiga in a more modern way, for real 2011 stuff (like modern media files, Internet, etc), where new features and high performance is more important than 100% backwards compatibility, you should look at the "NG" options:
3 – If what you want is an OS that runs on x86 (even if only "hosted"), is free and open, then AROS is the only option.
4 – If you are prepared to pay a little money for your hobby (for HW and OS), and what you want is the NG OS that has the best features, the most features, all big Amiga standards (Poseidon USB, Cybergraphics, MUI4, etc) not only included but *integrated*, best Amiga compatibility, etc, then MorphOS is the only option.
Hope that helps!
