While I agree with Keefy up to a point my money would be on the latest SL you could buy. The MK1 would be the one to buy if you just want to leave it sitting in your living room but these bikes are simply too good on the road to do that to them.
As well as the stuff mentioned they can also suffer from cracked frames by the headstock (apparently becoming more common as time passes...), cracked ally swingarms, broken head studs and the usual Italian charging gremlins. All are easily fixed, If not necessarily cheaply... As time went by each successive model fixed more of the problems until you get to the FE which was basically a SL with silver paint.
On the (right) road anything is possible and it's only when you get long straights that you find the bikes limitations (just about all IL4s bugger off). Bike's are geared as standard for 132mph but are massively over geared as standard and benefit from 2-3+ teeth extra on the rear sprocket.
Only thing more that I'd want for my MK4 would be another 15hp... "Need more power Cap'n..........."
Darren