My bike came with a Shimano "mutt" group -- some Sora, some Tiagra, some 2200. I considered a Campy upgrade, because I've ridden Campy before, but it seemed like just too much for a Trek 1000. I went with Tiagra because it was the highest Shimano group that was already installed (in part) on my bike, it's a quality group, and it hasn't been too expensive to bring the Sora and 2200 components to that level.

Granted, I still have to do brifters and cranks which are the most expensive of the lot. Even so, it's been an inexpensive and painless upgrade, the bike rides all the better for it, and I like it.