I have used both Bar&Pipes and OctaMED. Bars & Pipes is an extremely feature-rich, easy to use sequencer that is very "organic" seeming. It works very sensibly, and the music is displayed as coloured flowing lines on each "pipe/track". Bars & Pipes works for almost any type of music, whereas Octamed, because if its step-sequencer nature, is much better for mechanical type music, like acid, trace, video game music, etc. Although I have heard some good "organic" type music done on Octamed, you really have to know the program well.
Bars & Pipes, on the other hand, is great for doing music with flowing morphing tempos, time signatures, even free-form music with no set tempo or time signature.
I have three basic synths/modules hooked to my Amiga. A Roland Juno-106, a Yamaha TX-81z, and a Roland Soundcanvas SC-155. I think this is a great setup: analogue sounds from the Juno, classic 80's sharp FM digital sounds from the TX-81z, and a whole palate of useable acoustic, synthy, and percussion sounds from the SoundCanvas. If I had to only have ONE module, I'd probably choose a Soundcanvas.
If you can't find a Yamaha TX-81z, then a DX-21, DX-100 or an FB-01 can get similar sounds for cheap (the last module often goes for $50-$75US on Ebay - and it's 8-part multi-timbral!)
My Soundcanvas is an older one, and so can be acquired cheaply now. It can play up to 16 different voices at once (so you can do all your bass, rythm, melody, etc. parts with one device). Although they are GM sounds, they are pretty good/warm sounding, and there are about 125 extra MT-32 sounds too. The piano sounds are fairly realistic. Good value for the money.
The great thing about B&P also is that you can control your synth patches from within it, and even link it to an external digital multitracker so it runs in sync. I have mine synced with my Yamaha MD-8 minidisc recorder, so I can add 8 tracks of recorded audio (i.e. vocals, acoustic instruments) and they will lock to the MIDI instruments.
The sample triggering features on B&P are basic though. Good for doing a simple trigger now and then, but not multiple sample parts. OctaMED is MUCH better for doing music with sound samples.
Here is a link to some music I have created on the Amiga with this setup. B&P was used on all the songs except for "I Blame You", which was done with OctaMED.
http://tinyurl.com/qbetv
