For me it is wordreference. For example you look at one verb, and after they propose all the possibility to use. They say to you the principals translations , and then the compound forms. Just have a look, for me it is the best one : http://www.wordreference.com/fren/%C3%AAtre

1) http://www.collinsdictionary.com/dictionary/french-english 2) http://www.larousse.com/en/dictionaries/english-french 3) http://www.linguee.com/english-french

Definitely Ox.Conc.En.Dict ( Concise Oxford English Dictionary) I'm using this dictionary .If you want to download, you can find here. https://play.google.com/store/search?q=oxford