In the main game none of the choices you make will affect the achievements, and the few times when a certain answer may cause a slightly different development of secondary events you can choose whatever you prefer (the gamer's logic is enough to make a better choice if someone asks if you want help then you should probably say 'Yes' - it's not rocket science).
Keep in mind that there is a lot of multi-choice dialogues in the game, and most of the time what you choose doesn't affect anything (the typical choices are between some optional info and the choice that makes you progress the latter will continue to appear until you pick it), or don't have an impact on the main quest development anyway.
