I'll start by saying I'm a weird guy.

A long time ago I realized that people mean different things when they say 'priority'. If you only mean the 'value' of a certain task, then that's not a good way to prioritize, IMHO.

I've changed my model to prioritize strictly according to return on investment. I.e., how much value I or the company receives for unit of work.

In my professional project management and in my company, here's the algorithm that I pretty much use for every sort of task prioritization:

(1) I put together a list of items

(2) I put a relative cost (RC or C) associated with each item-- for a task list this tends just to be the hours you predict you'll spend.

(3) I hide those costs and then add some number that represents the relative business value (RBV or BV) of each item. (More on this in a second)

(4) I unhide things and then put another column that just calculates RBV/RC which indicates the return on investment (ROI) for each task.

(5) I then sort it all by ROI and work my way down the list in ROI priority order, always working on the tasks that offer the most ROI, I adjust values and costs (and re-sort) as my needs change, work completes, and as my understanding of each task changes.

The units used to value each assigned task is not really important. It's only important that tasks have a value that makes sense relative to each other.

For example, if I have these tasks:

  * Setup tech support email account
  * Improve usability for site logon page
  * Write a blog article about our recent features

I might then give these costs:

     01 hour  - Write a blog article about our recent features
     01 hour  - Setup tech support email account
     16 hours - Improve usability for site logon page

Having a tech support email account, I know that's important and I must have it, so it gets a high value. In this case, I'd say "Improving usability" is something we could survive without, but I firmly believe it could increase our revenue.

I might then give these relative business values (I'll just say points):

      200 pts - Write a blog article about our recent features
    10000 pts - Setup tech support email account
     5000 pts - Improve usability for site logon page

When I calculate the ROI and sort them, I get this list that I work from top to bottom:

    10000 pts/h - Setup tech support email account
      313 pts/h - Improve usability for site logon page
      200 pts/h - Write a blog article about our recent features

As long as when I add new tasks, I evaluate them against the other values and costs to ensure they're all relatively correct, the list always sorts to provide the tasks with the 'biggest bang for the buck' at the top.