Search is your friend. But you don't even have to search. These have been discussed in several threads in the last month. Just the first three pages include:
Roland BK-7 vs. AT350c
Roland Organ Question
Organs of the Nineties and Naughties (we beat it vigorously on that one)
New At-900 Platinum Edition
Atielier now under the Rodgers Umbrella
Listening to the forum members discuss this will give you a much better answer. However, we always try and support new members so you'll get direct answers too. Here's mine (every word of which will probably be found in the referenced articles):
The biggest thing Atelier has going for it is that this is a current product in production by Roland of Japan. That can only be said of a trifling few of the organs discussed on the HOME ORGANS section. Due to Roland's enormous digital synthesizer manufacturing and development division, the Ateliers are extremely up to date. I'd say that their technology is only about six years behind the synthesizer industry, which is like YESTERDAY in the organ biz. To give you an example, they recently (2007, I believe) discovered that there were solid state alternatives to the 3.5" floppy disk. They skipped over the SMART MEDIA CARD, the COMPACT FLASH, etc., even the MICRO SD and caroomed right to the USB thumb drive. In the US, the only other current available model is Lowrey. There are some new models just now appearing in Europe and Asia that look interesting but I would say that you can still count on one hand what's in production.
Atelier is largely a preset organ where ensemble sounds are concerned. That refers to diapason choruses for classical organ, tibia chorus for theater, and the various drawbar combinations for Hammond. The current series DOES give you drawbars and I haven't checked to see if they handle tibia and diapason too. The top of the line model, the AT-90 and AT-90s lets you select the FLUTE, TIBIA, or DIAPASON and let's you switch in each footage, giving you either a 0 or an 8. This probably only makes sense if you've played a Hammond before. The AT-90SL has virtual drawbars on the touchscreen. Maybe the s does also. I have one but never used the feature. The AT-900 and most of the models below it uses for-gosh-real drawbars. Classical and theater reeds are generally available individually but only from a menu whereby they can indeed be assigned to a panel button for live selection. When you use the orchestra sounds, you get most of the panel button choices, including piano, strings, brass, harp, marimba, etc. All in the home organ manufacturing business are of the belief that what most of us want are modern realistic sounds and that those theater and classical aficionados would probably buy an Allen, Rodgers, or Walker to get authentic panel layouts. I happen to be in that group and hence love the Atelier. Since ORGAN FORUM has subgroups for both theater and classical, you may perhaps assume that most on the home organ group feel similarly. Atelier can easily fool most listeners into thinking it has pipes but the organist is keenly aware of the compromises in setting up the sounds.
They are fairly reliable but certainly not unbreakable. I just blew the fuses on my At-90s subwoofer amplifier and am probably looking at buying a PCB for a couple of hundred dollars. Like a luxury car, the used price differs by anywhere from half to a tenth of the new price for all but the latest series.