Phil,
There are only a few folk on here that can properly give you their opinion on this (those who have owned both)
S2's are more comfortable, and have an interior but the drive is, in my opinion, less involving, it's just slightly bland in comparison.
On the other hand, the S1 is harder to get in and out off, the roof takes an age to get on and off, and is generally less water tight than the S2.
The S1 does on the other hand have a tremendous heater, so if you can get the car watertight then there's no reason why you can't use the car everyday of the year.
Being a bit of a lard arse - I would always go for an S2 for the easy of entry and for the interior finish.
From a pure drivers point of view - I prefer the S1.
horses for courses I suppose
Mac