The Nikon d5100 is probably the best new camera going for £600 at the moment - it has better noise characteristics than the 550d/600d, and in other areas they're a wash from what I've seen. Lens wise, the off-brands have the cheap wide zooms. I had the Sigma and it did really well.
The 5d classic will probably have better image quality but the tiny LCD and ancient focusing system would be the limiting factor. It also lacks video, if that is important to you. However, if you go this route you could make use of one of the best bang-for-buck lenses Canon makes, the 17-40mm f4 L, at the wide end.
The Nikon d5100 is probably the best new camera going for £600 at the moment - it has better noise characteristics than the 550d/600d, and in other areas they're a wash from what I've seen. Lens wise, the off-brands have the cheap wide zooms. I had the Sigma and it did really well.
The 5d classic will probably have better image quality but the tiny LCD and ancient focusing system would be the limiting factor. It also lacks video, if that is important to you. However, if you go this route you could make use of one of the best bang-for-buck lenses Canon makes, the 17-40mm f4 L, at the wide end.