The RS1600i is the best Escort set up from what I can gather. The S2 set up is pretty poor in comparison to the RSi and S1 set ups as they were designed for rally use where as the S2 wasn't. The main advantage of the RSi and S1 set ups is that they offer adjustment to the caster. The RSi is slighty better than the S1 set up as the mounting on the RSi is a one peice aluminium unit where as the S1 uses a heavy 3 peice cast iron mount.
The RSi also uses a different style joint to the S1 where the tie bar arm mounts the the mounting plate which I was told was stronger and less prone to dust and dirt.