In reply to ods: I have a Climbing Factory Groundhog and a mate owns one of the smaller Craghogs. The foam is decent quality, the price is keen and they're made here in the UK.
Based purely on the experience of our two pads, I'd have to say that the straps are a weak point: we've both had the stitching at the end of one (where it attaches to a plastic clip, which fastens to the pad). To be fair, it's repairable, but I've not had this problem with any other pad I've owned. On the whole though, they're good pads.
A few people I know have DMM pads. They're happy with them and my impression is that they're very well thought out and high quality (and you pay extra for it).
Don't know anything about Black Diamond Drop Zones. If I was in the market for a new pad now I'd be considering either of the above, or something from Moon, POD or Wild Country - all made in the UK (AFAIK), good quality and largely designed with British conditions - mud - in mind!