The Amig 1200 or the 4000 are your best choices if your looking to do all that the Amiga was made to do. The A4000 would be my first choice as it has the most options including AGA but a drawback is that there are only a fuw eccelorators available for it where the 1200 have more choices.
The 4000 also alows you to tap into the Video Editing end of the Amiga with the Video Toaster and Flyer.
Getting a used Amiga One is almost impossible and it has trouble emulating the older Amiga OS for playing games and things like that Building one would also cost way more then just getting an A1200(T) or 4000(T) "T for tower".
