Hi,
I used to write music a lot with my A1200. I used it as a MIDI seqencer almost entirely, with very little sample playback. A lot of people who do tracker sequencing use mostly samples. You probably are very familiar with the Amiga sounds, so know what to expect from working with samples. It is a retro lo-fi kind of sound.
I used a program called Music-X 2.0. I liked the MIDI sequencing on this. It felt untuitive for me. I tried just about every sequencer that was ever released for Amiga. Unfortunately, Music-X was never released as a freeby, unlike BarsNPipes or Octamed. Music-X also does not provide easy access to multiple MIDI banks (basically, 16 MIDI channels, though it can do more with the right hardware/drivers). BarsNPipes has an open source 3 bank MIDI interface (3x16=48 channels).
I think it is worth trying a few different programs, before really focussing on just one, and investing a lot of effort into a particular way of working.
There are also some dedicated sound generators/software synths for Amiga. Some of these are pretty decent, and in my opinion, really take good advantage of what the Amiga can offer to contemporary music production. If you like gritty, retro, game like, or lo-fi. This kind of sound character is often used in music.
I also think it is worth understanding what you will not get from music production with an Amiga. Modern computer music production has a lot to offer in terms of usability, versatility, community support, commercial support, sound fidelity, attractive interface, cheap and reliable hardware, expandability etc. You can of course use an Amiga as part of a modern studio setup, along with other computer tools.
What exactly are you looking to do with your music? Is your focus on writing finished pieces of music, or are you mainly just wanting to play around with the Amiga?