For my pro workflow I mainly use Photomechanic, Lightroom 4, PS CS6 and Alien Skin Exposure 4. All are great. The only one that I couldn't live without is LR4. All of these programs offer fully functioning demos. LR4 is extraordinarily good value.
If its ipad you want though, I've tried most apps and snapseed and VSCO rule. Even just snapseed on its own is brilliant. Made by nik software who've produced some great pro-level editors for PC/Mac. I've got 3 DSLRs, a Fuji X100 and a few great film cams... all I generally take with me on holiday/city breaks these days though is my iphone 5 and those 2 apps.