I am a bit surprised the "high resolution" group hasn't chimed in with a few 5Ds(R).
If money were no object, I would probably own:
- 1Dx II for times I wanted a high frame rate or times when resolution was not an issue.
- 5Ds(R) for times when I wanted all the resolution I could get
- 5DIV as my general everyday camera
If I could only have one, then the 5DIV, which is what I actually have.
The quick point here is that each body actually has a niche. It is always best to consider need and intended use when picking the body. For example, I have seen 1Dx go by for ~$2,500, 5DIII for $1,200-$1,500, 5DII's for ~$600, 5Ds(R)s for ~$1800-$2,000 and 6D I for <$1,000. All of those are good cameras that have taken many a great picture. As for a used FF body, if I was looking for the "best value" FF on the market, a good used 5DIII would be a great general camera. If you need the high FPS, then a 1DX, if budget is a concern, find the best 5DII or 6D I you can find. If high resolution, find a nice used 5Ds or 5Ds(R).