Hi Here's my opinion
Back in the day i started out with an a500 using "noisetracker" and later an early version of Octamed Soundstudio. eventually i upgraded to the a1200 and used Octamed Soundstudio on that almost exclusively. It has the tracker interface you are looking for - yet it has a lot more features not found in those earlier soundtracker programs such as MIDI, support for improved sound cards and a UI for creating "synth / chip" sounds plus a bunch of effects .
I used my amiga 1200 for many years cranking out tunes on the beast. Id have to reccommend based on my experience to go with the 1200 which has much better options for expansion. The only reason i retired the Amiga from the music studio was the arrival of the PC version of Octamed. This was short lived though as having later discovered Linux i removed windows from my life completely. Now i use Renoise on Ubuntu which is the best tracking software i've ever used (it almost seems wrong to call it a tracker) and many of the key bindings are the same as i was used to with Octamed.
Im not trying to put you off getting an amiga though - in fact im in the process of bringing mine back to life with some upgrades i could never afford in the day.
So ... unless you can afford one of the big box amigas - in my own personal opinion - grab an a1200. While you may have some compatibility issues with older software - it has more base memory to start with (2mb you will find even this is quite easy to fill up with decent quality samples) and you can still buy new expansions from the likes of amiga kit and vesalia. Octamed Soundstudio if you can find a copy is the only tracker you will ever need !
Heck -- i knew someone who ran an ST emulator on his amiga and used a very early version of cubase! (seems a bit extreme to me but there you have it)
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