What are some alternatives?
When comparing Amazing Marvin and Remember The Milk, you can also consider the following products
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
My Daily Planner - Organize your day with pen & paper. Free printable template.
Trello - Infinitely flexible. Incredibly easy to use. Great mobile apps. It's free. Trello keeps track of everything, from the big picture to the minute details.
Asana - Asana project management is an effort to re-imagine how we work together, through modern productivity software. Fast and versatile, Asana helps individuals and groups get more done.
Agenda - A date-focused note taking app for both planning and documenting your projects.
Toodledo - Toodledo provides a set of tools to increase the productivity.