My first thought was just saying "Google is better", period. But as I like to challenge my own beliefs, I made a search in both search engines to see what came up: "is yahoo better than google?"
Results were very similar and I've found these two articles that may light up some insights on the subject:
Surprise: Yahoo Is Now Actually Beating Google in traffic.
7 Things Yahoo Does Better than Google - Search Engine Journal
So the answer might be: Google's search engine is still far better than Yahoo but Yahoo, as a company, has some services that Google can't beat:
1. Yahoo Finance
2. Yahoo Answers : Q&A
3. Backlink Reporting via Yahoo Site Explorer
4. Flickr : Photo Uploading & Sharing
5. Local Search : Nuff Said
6. Entertainment
7. Privacy
Thank you for your question, I've learnt something in the way :)))