I only use online dictionaries. Dict.cc is good but very full of translations which can be hard to tease out sometimes; Leo isn't bad and has nice links to Etymology, Pons is good too. But depending on your level of proficiency, Duden is the best. It's not a translation dictionary but in my opinion is the real authority. Maybe I'm just old-fashioned. Plus all the explanations are in German, which I like because, even though I'm a native English speaker l, I hate the English language. Just my preference.