so far I have shimano 105 and some oldschool suntour 4050 Edge. Actually I am mixed ont he two...the shimano STI levers are hella nice, but my old suntour setup shifts better....all you hear is the click from the downtube shifter, and like silk, it's on the next gear.

The shimano is a bit slower to shift over, but it's not too bad of a shift....I just feel slightly disappointed spending the cash I did to get lower shifting performance than a 15 year old low-range suntour drivetrain.

Don't get me wrong, shimano isnt bad really...they do the same thing campy did...their standard or nothing. It's just how they design their stuff. From my understanding:

shimano:
STI lever hoods are thicker, and uncomfortable to some.
their use of ramped cogs give good shifting early on, but it degrades as they wear out (good to know when to swap them out I guess).

campagnolo:
Ergoshift levers have thinner hoods, so are more comfortable to some.
lack of ramping on gears, so you dont get the shifting advantages of shimano...however the cogs are all of uniform tooth design and thickness as a result (maybe this is why my suntour seems to shift better than my 105 group).