Iron kingdom
I've been running a D20 version for 7 years now, so it started before the IK system came out... well, 2nd edition or whatever. Never heard of Unleashed until I read this thread.
I've looked over both versions; don't see that much different. Slightly different numbers to crunch, but they should otherwise be compatible.
As I understand it, players seem to like one or the other, but not both. The concept and setting work either way.