El mas usado!

Im in Spain right now and this app has been the most used and allowed me so much depth of experience. Not only does it translate unknown words, but uses many in various phrases to give a much deeper depth of meaning (e.g. Look up "asi" to see how many different uses of the word there are). It also does a great job of showing which uses tend to be used more in Latin America or Spain. Yes, the most expensive app Ive bought and no doubt worth it :)

Canada in España about Collins Spanish-English, v1.5.1