I'm a big fan of online translators, not only because I'm interested in languages in general, but also because they make my work easier every day. Google Translator has been sitting on my Bookmarks Toolbar for a long time, as it is the translating service I use more often. However I recently found out that Microsoft's Bing has launched its own translating tool, so I decided to give it a go. You have to try things before judging them, don't you?
The first obvious difference between Google and Bing is precisely their translating powers: while the first supports more than 50 different languages, the latter features only 20. But the truth is that when Google Translator was launched it didn't support that many languages either, so I wouldn't be surprised to see Bing Translator adding more languages in the future.
One thing I love about Google Translator is its ability to detect source language automatically, so I don't have to select it every time I use it. Luckily Bing Translator offers the same functionality. Also, besides direct translations, both Google and Bing offer some extra tools, such as a widget to offer a translated version of your website (both), a special utility to perform translated searches (Google only) or a translating bot to assist you in multi-language chats (Bing only).
Now, what about translations themselves? Honestly, I didn't find much differences between them in my tests. I tried several language combinations with Spanish, English, German and Italian, using different texts and swapping the source and target languages in order to test the translating engines. The results were surprisingly similar, in both ways: when Google Translator obtains a good translation, so does Bing; and when Bing produces a completely absurd text, Google doesn't succeed either.
Oddly enough, both seem to be better at translating into English: as soon as you pick another target language, results are a bit distorted. Both are also equally fast: you hardly have to wait for more than 5 seconds to have your text translated. The only difference I noticed, if any, is that Bing seems to be slightly better at certain expressions, providing you with the correct translation instead of a meaningless word-by-word equivalent.
Generally speaking though, both Google and Bing feature similarly powerful translating engines. So if you work with different languages on a daily basis and need to do frequent translations, I'd suggest you take advantage of both of them!