I had good luck with Printer Pro which requires a helper application running on the Mac computer in order to get to the printer itself but I could print from pretty much anywhere I had a data connection. There was sometimes a considerable (minutes to hours) lag between executing the print command on the iOS device and the actual printing occurring and not all document formats are supported. The supported formats are PDF, Word, Excel, Powerpoint, Pages, Numbers, Keynote, TXT, HTML, JPG, and webarchive. There is also a Printer Lite from the same publisher, but I have no idea what is left out of the Lite version.
I haven't used Printer Pro in some time now because I got a Brother printer with built-in WiFi and since then I have used the Brother printing app and it is great as long as the printer is on the same WiFi network. Epson has similar iOS apps for its wireless printers which I would assume would work equally well.
