I have been wanting a solid app for cryptocurrency trading for years now! I'm shocked that the likes of Bittrex and Poloniex have not come up with their own. Something that runs on the PC etc.
But given that is probably not happening soon enough, I like Poloniex's system the best. Metatrader is looking good too, though yet to use it!
It's not that shocking really - they have a (full-time) job running an exchange...
They could certainly hire developers to make full fledged apps. I'm sure the large exchanges have pretty decent revenues.
as @cattyboy shared above,
https://www.coinigy.com looks like a really great option. $15/month, but looks impressive at first glance...