Why should I use Amiga?

[Tomas]

I was considering AROS, what would you recommend I use? How does the Amiga forever thing compare (I perfer Free (as in freedom))?

Aros has absolutely nothing now in terms of software base compared to AmigaOS 3.x, 4.0 and MorphOS. I only recommend Aros if you yourself want to spend time improving it by developing software or improving upon Aros itself. It is just not ready for end users yet.

Amiga Forever is basically just a emulator package which includes the classic AmigaOS, so it wont be the same as running it native.

[Tomas]

What hardware can I run 3.9 on?

Only on the classic range. I recommend a upgraded a1200, a4000 or a a3000 for this purpose. Plenty of these sells on ebay.
You can also run it under the emulator uae/amigaforver.