The second one is also EX series which is top of the sigma range.

I didn't think that either of them are specifically designed as such for digital. Just that they are both compatible with EOS and Digital EOS.

Would I pay 100 quid more ? Yes I probably would.

My current EX 15mm fisheye is a superbly built bit of kit and give me excellent results. I've used with my 300d, 350d and 20D and it's not specifically designed for digital use.

To quote Sigma

"DG Lens. These are large-aperature lenses with wide angles and short minimum focusing distances. With an abundance of peripheral illumination, they are ideal lenses for Digital SLR cameras."

Whereas,

DC Lens. These are special lenses designed so that the image circle matches the smaller size of the image sensor of most digital SLR cameras. Their specialized design gives these lenses the ideal properties for digital cameras, including compac and lightweight construction.  ie, like an ef/s lens.

Remember that they are also circular fisheye's and not full frame, although on digital, I imagine some of the circle will be cout out due to the sensor size. I think the full frame sigma fisheye is 15mm.

I would always go for EX lenses in the Sigma range over the non EX versions.