S1 3.0L has a 232 bhp version, from a European Fords
S2 3.0L has 205 bhp version from a Ford Escape Truck in the USA
S3 is the 3.7, not sure where it is from...
S1 gearbox is faster than the S2, which is a bit slow and ponderous. The S3 is a Mazda box and it is fast and short movement.
The S1 engine is possible the best of the older cars. The S3 is great, but some report a slow engine response, sometimes described as a "hanging throttle". It is an engine management issue and at the moment there is no easy answer.
Availability: the S3 is new, so you can have what you want. The older S1 and S2 are not that common and it can take time to find a good one.
Possibly not the most helpful reply...
