In my view, most of the apps available are way more complex than they need to be. My recommendation is to look for an app that has a very clean, simple and intuitive interface that won't slow you down when entering tasks.
I've tried Nirvana - in my view it's too complex. Same with Toodledo and although it allows you to turn off fields, it's a poorly designed interface that isn't easy to use.
I'm using Appigo's Todo but am dissatisfied that it's getting more complex over time with additional fields that I have to scroll past when entering tasks.