When comparing Nirvana vs Casual, the Slant community recommends Nirvana for most people. In the question“What are the best cross-platform task apps?” Nirvana is ranked 49th while Casual is ranked 67th. The most important reason people chose Nirvana is:
Designed specifically for the Getting Things Done methodology as created by David Allen.
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 Tracks task dependencies using a graph
Pro Great to-do templates
Every to-do list & project can be saved as an amazing template that you can re-use in the future.
Pro Offers a high-level overview of projects
The workflow with dependencies shows where the things are at a glance. No more frustrations of how your project is going and who is doing what.
Pro Sync deadlines to Google Calendar
To-do items can be integrated with your day-to-day schedule using Google Calendar.
Pro Visual way of organizing your work
The workflow includes dependencies and shows you where things are at a glance.
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 Price
At its cheapest level, Casual is $9 per month for two users and two GB of storage. The trial period is short and there is no free version.
