OK I'll start with a disclosure. I don't ride a bike with either type of brifter but I have tried out a few in the shops and with my small hands I found the Campagnolo brifters to be quite good. The Shimano ST-R600's aren't different in anyway from their regular ones except for a small shim that reduces lever travel.
Something I've noticed is that Shimano brifters mount on the handlebars in such a way that the body is angled upwards. Campagnolo brifters mount with the body of the brifter more or less parrallel with the ground. This difference I believe plays an important role in how they feel.
Regards, Anthony