General opinion is that Campag brakes provide more progressive, powerful braking - whereas Shimano are more ON-OFF. However, Campag brake calipers don't have a QR on the caliper - so can be a little bit more fiddly for wheel removal if using wider tyres. Don't under-estimate the need for brakes on a tri-bike either - courses can often be more technical than a typical TT course and if your weights all up-front on a tri-bike, handling under braking can be pretty iffy.