s1 for looks and power(im biased as ive got one)
rs1600i for a decent car but bear in mind both will have loads of problems/hard parts to get hold of if they go wrong
if you prefer the s1 to buy try other places rather than pf/autotrader...etc as they will price them up even if they are doggy
take someone with you that knows mk3's inside and out regardless of rs1600i/s1