When comparing Nirvana vs Taskwarrior, the Slant community recommends Taskwarrior for most people. In the question“What are the best cross-platform task apps?” Taskwarrior is ranked 2nd while Nirvana is ranked 49th. The most important reason people chose Taskwarrior is:
The command line interface puts powerful filtering expressions, context, annotations, tags, due dates, reoccurrence, and user-defined-attributes totally in your hands. It’s fast and low friction.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Streamlined for Getting Things Done
Designed specifically for the Getting Things Done methodology as created by David Allen.
Pro One of only few faithful implementation of GTD approach
The Nirvana approach is one of the few that successfully encapsulates the spirit of Getting Things Done.
Pro Flexible structure for simple to complex usages and workflows
Pro Clean layout
It has a very simple, understated design.
Pro Useful history of actions
Nirvana offers a chronological look at completed tasks that is good for reporting and improving future estimations. That said, it could be improved by incorporating a true journal view rather than a simple list broken up by week.

Pro Command line interface
The command line interface puts powerful filtering expressions, context, annotations, tags, due dates, reoccurrence, and user-defined-attributes totally in your hands. It’s fast and low friction.
Pro Extensible
Taskwarrior has many front-ends, services, extensions, hook scripts, and capsules available. Taskwarrior keeps a list of contributed tools on their site.
Pro Lightweight and fast
Taskwarrior is written in the speedy C++ language.
Pro Tasks stored in plain text files locally
Future-proof and easily integrated with version control system. You never lose access to your data.

Pro Sync across devices
When used in conjunction with the Taskserver, it can sync tasks (conflict-free) across your Taskwarrior devices. This includes integration with Mirakel.

Pro Supported internationally
It has UTF8 support and is translated into many languages.
Pro Customizability
Taskworrior allows you to define custom attributes and reports to your needs.
Pro Self-hosted Taskserver
You can be in full control of your data.
Cons
Con No native OS X & Windows apps
There are currently no native apps for Windows or OS X, although the company has claimed to be working on them.
Con The Pro service tier still does not have common features
Common features such as notifications and sharing between applications aren't available, even in the Pro-tier. Its only native integration with other applications is adding tasks via a specialized email address generated for your account.
Con Command line interface
A command line interface is a arguably overly verbose, consequently tedious, way to interact with a To Do list.
