I like having purely flavour dialogue choices because they change the narrative (however slightly) and my perception of the character(s), especially if the next couple lines of dialogue respond to the choice I made.
I'd like at some point in the game to have a couple of meaningful choices though. Another thing with the flavour choices is that there shouldn't be way too many of them imho. A game that does flavour choices well is
Price of Power, if you want to see what I'm talking about.
Other than that, what clockwork gnome said.