The eternal deabte dredged up from years ago
Can I say Mavic?
Both are pretty good now. Through most of the 90s though the big S was ahead really. I started in mountain bikes so favour Shimano. I also have to say I favour it because it's slighty 'uncool' in roadie circles. Nothing raises a wry grin more than the chap out on the club run on his Taiwanese plastic bike with Campag Daytona bashing shimano for being souless.
Durability? I have an original 9 speed ultegra gruppo (reknowned for its unreliability) with 1000s of miles on it, must be well over 15000.