Id be going the SK group buy stuff. Just go look at his suspension 101 which is stickied in the suspension section. He has the pictures of the valves from a mono shock, and a twin tube (twin tube = japanese coilover). From that alone you cant seriously look at any other option.
And Im guessing Im probably the only person on here who has had full madcore jap shocks, then to the same jap shocks rebuilt but with lower spring rates, then to the same spring rates in the orginal coilover casing with the bilstein inserts. So that way I have had a direct comparison. Trust me, the bilsteins are the ONLY way to go, they are 100% better than shocks that were specifically rebuilt to suit the spring rates and my car.