I read various comments on Sora, Tiagra and 105. In general, the quality levels would be in that order. If you wanted to save money you could always go with Sora. I saw one comment one day where someone was saying these days every manufacturer have a decent level of quality. Guess you always test drive some though. I sat on a bunch of different bikes before I chose my hybrid to get a feel for the fit.
List of manufacturers:
http://en.wikipedia.org/wiki/List_of...ring_companies