Which is the best currency converter app for iOS? And why?

I'm one of the developer of Valuta EX (https://www.producthunt.com/post...) and I would like to know what do you search for in a currency converter app. Why would you prefer an app instead of googling? And how would you chose among two currency converter apps? Have you some apps do you like most? Why?
Product Marketing
@federico_badini I use converters pretty often as I travel a lot. Googling on mobile is not as handy as a standalone app 9maybe just because I like to have an app for everything 😀). Most converter apps are pretty similar, so it is hard to name one fav. The action itself is pretty basic, so it is hard to outstand. Though I was thinking of something close to what Chronos app is doing for time converting. Though would be relevant for those travelers mostly, I guess. And checked Valuta EX now, looks pretty good, I would use it.
Digital Strategist
@federico_badini for a longtime I used Convert by taptaptap (now LateNite Apps). Convert not only did currency conversion but other unit conversions as well. The app had one of the finest UX when it was released. I currency use Elk, it's simple and straight forward. I like simplicity, ease of use and having the latest/accurate rates in conversion. Most important, the ease of changing currency in a snap would make be download/buy an app. Hope this helps!
iOS Developer
@federico_badini Elk, primarily because of the design. I only really ever use currency conversion apps when doing multiple conversions between two currencies (like planning for a trip). 90% of the time I just use google or voice (Siri, Alexa, etc) for convenience and natural language processing.
Dir. of User Experience @SSCTechnologies
@federico_badini The mac app Soulver is an app I use almost daily because it's better than a calculator and easier than Excel for many things. It also happens to be a great currency converter (they also have iOS app): http://www.acqualia.com/soulver/