The Technomancer companions play a critical role in your journey around Mars. The side quests they give are a nice way to get additional experience and items. They've got your back in combat and prevent you from getting swarmed (as much.) Their passive abilities, such as boosting your Talents, are also nice.
And last but not least -- what self-respecting open RPG doesn't include multiple romance options?
This short guide will help you get a feel for each companion's strengths and weaknesses, along with their overall personalities.
First up: David Ward.