I list my preferences for online translators in The Best Reference Websites For English Language Learners, along with sharing research from The New York Times on which ones do a better job. I list Google as the best.
Ethan Shen has just done a research project comparing Google Translate, Babelfish and Bing Translator. Here are his conclusions:
The final data reveals that while Google Translate is widely preferred when translating long passages, Microsoft Bing Translator and Yahoo Babelfish often produce better translations for phrases below 140 characters.
Does that reflect your own experience?