In reply to thelostjockey:
I don't have Achilles issues, but I have an (30 years old) compound heel fracture. Hokas are the only shoes I can run in (and I run exclusively off-road, as it doesn't knacker my ankle)
Challangers are really nice light comfortable shoes, but the sole construction is not that hardy. So they are fine if you want to run on gentle trails and footpaths.
If you are going to go out onto more rugged and rocky terrain (say the Snowdon Horseshoe), then they won't last. For rugged terrain, I would recommend Speedgoats - they are a brilliant all-mountain shoe. I've used them on most of the big ultras I have run, and have never had a problem.
Steve