I've used three different ones, and Google is about the best of the free ones I've found.
When translating from Italian to English, you can get a pretty decent idea of what is written.
But when translating from English to Italian, I reverse translate it, to see what doesn't translate accurately. I then re-write until I can get a pretty clean translation both ways. I find you get the best results when you write in short, simple sentences, preferably with words that don't have dual meanings.