I recently tried several printing apps and finally settled upon "Printing" made by Ndili Technologies Inc.
Theirs was the only app that I got to work consistently across different networks. The app let's you discover bonjour printers or enter their IP address and then download the specific driver for that printer if you need to.
They have a free test app to see if it would work for you.
It's not the prettiest app but it works for me. I just wish Readdle's Printer Pro app would receive an update to have the same functionality of Printing because I like the look of Readdle's's app better.