Pretty much all of the systems have their strengths and weaknesses. I am not too big a fan of putting the wheels in the Ketron position (quite a lot of 88 controllers put them there, too) as, especially for the arranger player, getting to it and getting back to the keyboard involves far more distance than at the end of the keybed.
Roland have a very good system, one I've got used to over the years, but it has one fatal flaw... if you use the lever for modulation, it always returns to zero when you let your hand off. Now, this is great for note vibrato (you don't tend to want to leave it on all the time) but it is terrible when modulation is used on say the filter cutoff, or to crossfade between fast and slow Leslie samples of an organ, etc..
Unfortunately, this is EXACTLY what Roland have done, especially in regard to the Prelude and GW-8. There are a lot of patches that modulation does timbral things rather than vibrato, and sadly, no way to do it from any other controller. The problem is that these arrangers are derived from the Sonic Cell module, which is designed to be run from a MIDI controller keyboard. And most of THESE have sliders as well as levers or wheels for modulation. So, even if you have a controller with a Roland or Korg paddle/joystick, you can still set the modulation with a slider. On the G70/E80, most of the patches that do this have been programmed so a slider can be used (but it doesn't send mod commands, it's different controller# and the patches are written for it). But unfortunately, a lot of the SRX cards have the same issue... and the slider can't address them.
Somebody at Roland is asleep at the wheel
If you have a GW-8, I suggest a call to Roland. It would only take a minor OS fix to task the mod command to one of the 'analog modify' knobs and you would be in business. But without this, quite a few patches lose at least half of their usefulness (although, use them in style or SMF mode, and you can program the mod values in - it makes for some excellent organ parts in some of the styles).
I've already posted about how great pitch strips are... love 'em! (had a CS60 back in the day, too - first thing I played with a strip). I kind of prefer Korg's paddle to the Roland one because up/down can have a different negative function to the positive direction, and it has better resolution, plus my Triton has paddle AND strip - best of both worlds. But, push comes to shove, I think the K2500 has the best possible system. Wheels, small strip AND large strip, tons of faders buttons and keypads, and an OS that allows you to basically make any of them do anything whatsoever, no matter HOW whacked out your twisted mind can imagine you need!
But I always come back to the Achilles Heel of the arranger... no matter HOW good and sophisticated the LH controllers get, you can only pay them lip service because of the primary need to keep inputting the chords, no matter HOW repetitive they are. Most of the juiciest times to do bends is EXACTLY when you need to make a chord change. What's a boy to do? Foot bends (even for those lucky enough to have an OS that allows them) are generally in one direction only. We'd all bitch like hell if the pitch bend wheel or lever only went up OR down! And your feet are pretty busy already... (at least, mine are!)
Some way of handing this task off (playing the chords of a repetitive section) really needs to be introduced (or 'reintroduced'
) before we can start to impart the expressiveness that those working with SMF's or MP3 tracks have at their LH's command...