To give you a little background...

I write communications software (mostly c# and c++) for a relatively small company that is used primarily to read historical data from oilfield flow computers and data from PLCs through various protocols. I've done this for about a year and I enjoy the work but graphics have always fascinated me and I would like to do it for a living sometime in the distant future. Over the last months I have been experimenting with 3d graphics via XNA and have mastered some of the basics (rendering terrain, water, camera control, etc.).

My question is...what is the best way to start a portfolio? Would a prospective employer be more impressed by a complete and working game (made with something like a top-down cookie-cutter similar to Unity) or a small clever 3d game (from the bottom up with raw OpenGL, DirectX or XNA)? Based on my short experience writing a 3d game of any size is rather overwhelming...and while I'd gain experience either way I'm not sure how to best use my rather limited time (about 1 hour a day).

Any advice on which direction to take?

Achieve either and you will be off to a fine start! Ultimately it may depend on the specific job that you are applying for as to which type of project would be more appealing.

Here are some more general tips for completing a portfolio as well: http://www.ineedtomakegames.com/how-to-get-a-job-in-gaming/2012/2/19/step-6-resume-and-online-portfolio.html

Best,

Destin