If it's the 1Ds Classic that you are referring to, then I would assume that amongst these choices, the 30D is the cheapest option, the 1DMK2N the most expensive, and the 1Ds is midway. I've never used the 1DMK2N, but have used the other two...the 30D for a casual wedding shoot and the 1Ds currently as my only camera body.
The 30D is plenty for a lot of people and some paid wedding photographers do use this camera. This, and the 1DMK2N have generally very low noise levels at all ISOs and are hence suited to low-light work if you're not using a flash. I've read elsewhere that the 1Ds is a 'strobist' camera. That is, if you're into studio work with controlled lighting, don't need super-fast write times and frame rates, or shoot with a flash (which would limit how fast you can shoot the next shot), then the 1Ds is a great camera.
Without flash and in low light conditions, you'll need to be extra careful with the 1Ds to avoid underexposure, otherwise noise may be an issue. However to be frank, unless you're extremely intolerant of noise, this camera actually does produce results that are more than acceptable. Noise and speed would be the main 'cons' of the 1Ds. Resolution is it's key strength...having great resolution, excellent 100% viewfinder, great build and AF in a single body and relatively cheap, makes a tempting package.
In terms of resolution, I wouldn't be surprised (and may even take a leap to say this) that the 1Ds is leaps and bounds above the other two cameras. If you look at the comparison images in DPReview's 1DMK2 review, you'll see the amazing difference between the 1D2 and the 1Ds. The 1D2 images would in turn mirror the results that you're likely to get from a 30D or 1DMK2N. I still take the same artistically-terrible pictures that I was making about 5 years ago, but whenever people see my 1Ds images, their comment is invariably, 'Wow, the images are so clear!'
In the end, it's hard to answer the question for you. All the extra resolution of the 1Ds comes to moot if you're only going to be doing small prints. In terms of ease of use, the 30D would probably come out tops. The 1DMK2N is the 'best balance' between performance, build and IQ. The 1Ds is...well, tops for image quality. So it really depends on where your priorities are. Personally I do plenty of landscapes and need needle-sharp detail, and don't need speed, but rather, do things methodically. If this is the route you also take, the 1Ds would be an excellent camera. I think it is in fact, a tremendously underrated machine.
To the majority of people, the 5D has pretty much eclipsed the 1Ds. I think you should look into the 5D as well...if only to confuse yourself further. 
If you're strapped for cash, get a 30D and go for glass and lighting equipment. Heck, even I have considered on a few occasions to downgrade to a 30D. If your lens setup is in serious need for a change, then sometimes the camera body has to give. However bear in mind that the lens choices for each camera body will be different. A 24-70mm would be excellent on a 1Ds, very usable still on a 1DMK2N, but on a 30D the focal length range may not be so hot.
EDIT: And before I forget, I shoot exclusively RAW with the 1Ds, which gives me much scope for adjustment on computer at a later stage, plus it maximizes the results I can get. This is not something for everyone, so you may want to factor this into the decision as well. Somehow, I don't trust JPEGs anymore ever since I've tried shooting RAW.