IMHO either Genuine Porsche or SuperFlex.
A good upgrade on any 944 S2 are the 968 castor mounts, which are actually under a Porsche Technical Service Bulletin for those who have gone to 17" wheels. You can get these from Hartech as well as other specialists, but I'd check OPC's price first. I *think* the quality of the Porsche stuff may be better though. I know that mine were beginning to perish but still be intact on my 951 and they can't have been more than 6 years old then, which some may see as acceptable for the price mind you

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My S2 became far more predictable with the new castor mounts (they are basically front wishbone rear bushes, but they also serve as an adjustment for the castor.
The one thing I would recommend is new nylocs of the appropriate treatment and grade for the mounts (e.g; Zinc or galvanised).
The only place I'd poly on a 944 would be the front ARB bushes. If they see oil from the PAS or more likely an oil change (the oil filter is in a frankly stupid location!) they won't swell unlike the rubber items.