I prefer http://www.dictionarist.com/
And chrome plug-in: you can double click on a word even if it is inflected form such as the word "sufrida" it can detect the root form "sufrieron", here is the chrome plug-in link:
https://chrome.google.com/webstore/detail/dictionarist-instant-dict/npggnghnhkgioladlpfehafajnghlklc