I won't recommend one retailer above the others, but I will give you feedback from readers:
A.T.: "I would prefer to buy my book from an outlet that ensures the author gets paid well enough to write the next book."
WU: "For me, it was a matter of the variety of formats. Smashwords was the perfect choice because I was able to get (for example) a pdf copy to carry on in my books repository in my laptop."
BOOKS FOR CONSULTANTS (AND OTHERS)
The Secrets of Consulting: A Guide to Giving and Getting Advice Successfully
More Secrets of Consulting: The Consultant's Tool Kit
Are Your Lights On?: How to Know What the Problem Really Is
Weinberg on Writing: The Fieldstone Method
THE QUALITY SOFTWARE SERIES
How Software is Built (Quality Software, Volume 1)
Why Software Gets in Trouble (Quality Software, Volume 2)
How to Observe Software Systems (Quality Software, Volume 3)
Responding to Significant Software Events (Quality Software, Volume 4)
Managing Yourself and Others (Quality Software, Volume 5)
Managing Teams Congruently (Quality Software, Volume 6)
Becoming a Change Artist (Quality Software, Volume 7)
CHANGE: Planned & Unplanned (Quality Software, Volume 8)
Change Done Well (Quality Software, Volume 9)
THE SYSTEMS THINKING SERIES
An Introduction to General Systems Thinking (Volume 1)
Passive Regulation: General Systems Design Principles (Volume 2)
Active Regulation: General Systems Design Principles (Volume 3)
Rethinking Systems Analysis and Design (Volume 4)
TECHNOLOGY/PSYCHOLOGY
The Psychology of Computer Programming
Exploring Requirements 1: Quality Before Design
Exploring Requirements 2: First Steps into Design
Perfect Software And Other Illusions About Testing
Roundtable on Technical Leadership
Roundtable on Project Management
Understanding the Professional Programmer
NOVELS: TECHNOLOGY LESSONS FRAMED IN FICTION.
The Residue Class Mysteries Series
Can naive mathematicians foil a sophisticated master criminal?
Where There's a Will, There's a Murder:
Can young geniuses stop the murders of potential billionaires?
The Stringers Series
Six special young people become a team to defeat an armed secessionist militia.
First Stringers cope with a dangerous Stringer from South America.
The Aremac Series
Two young inventors confront the problems accompanying fame.
Successful inventors assist in protecting an abused Navajo inventor.
Jigglers: Aremac a Century Later
(Aremac Power sequel, novelette)
Women of Power
Two people from different cultures, each with incredible powers, team up.
Earth's smartest living entity befriends humans to save itself from other humans.
Will a young woman's talent win her the freedom she lost when she lost both hands?