I have the Motif, the PA80 ( with the triton sound engine ) and have had several PSR boards as well.

Let me start with the sounds. This is of course VERY subjective but for me.... I have never placed a lot of emphasis or importance on the "sweet " or "cool" thing. What technical meanings do those terms have anyway ? Having said that, the sax and horn voices on the Motif aren't quite as good to me as those on the 9000. I am not sure if it is the sample itself or just the way synth parameters and effects are set between the 2 boards. If you're going to focus a lot on acoustic voices, particularly horns and reeds, the Motif may not have the best of them. Still, it has the best piano sample I've heard on any synth ( NO apologies to Kurzweil ), the best Rhodes sound I've heard as well. The acoustic guitars are outstanding. The drums are excellent. Organs are decent, but don't blow me away. For the few sounds I don't like, if I don't like the comparable sound better on my Korg PA80, my software sampling devices more than make up for it. Where this thing really shines is in synth voices too. I find synth editing in general to be a lot easier to understand and navigate as compared to Korg's way of doing it. I like Triton sounds, but I find that overall I favor the Motif's sounds. Of course each has its' strengths and weaknesses in the different instrument types

Control over arrangement ? The 9000 is an arranger, not a workstation, although it, like the PA80, has many workstation like features. A true arranger is a great place to start new ideas and hear it all together. The thing is, unless you modify the patterns in a sequencer, the patterns stay the same. Arps are dependent on the notes you play. As far as the arps and combis on the Motif, no they will not work in the same way as the Karma, with multiple arps or GE's
( which for lack of a better way to explain are basically algorithim driven, multi arps ). You can make a "performance that will include arp driven drums and play left hand bass and right hand rythym ./chords, but the Mo does not have patterns that respond to chord data as an arranger would ( or in a similar way to what the Karma does ). The arps are very useful for making phrases on each track that can be put together to make a song. The Motif suits me well because this is exactly how I prefer to compose. I prefer to work on one track a piece at a time and build it in a sequencer or... play the part in real time.

As far as the sequencer goes, it is great for chaining patterns together, and for making user arps and phrases, but for any real editing, the Mo is like any other synth sequencer.. that is... not comparable to the editing abilities of an external sequencer. Just as the PA80 sequencer is excellent for doing certain pattern specific operations, much better than an external, but as far as song creation and basic midi editing , it pales in comparison to the lesser versions of cakewalk sequencers and even a couple of the freeware ones.

I tried the Fantom and compared it to the Mo when I was looking for a new workstation. Since I already had an arranger my prioritiy was to focus more on the sounds and editing capabilities than the "accomp" or groove features. I think that both are very good workstations, and the Fantom is simple to navigate to boot. The Mo sounds just grabbed me a little more in the end. The same would be true for me if I compared the Motif vs the Triton, ( if I didn't already have the PA80. )