My take I think is a quite common one; The aim to tell the truth as long as possible, but still having the overall goal to winning each board I sit down to play on. Then, of course, you would have to define winning, which does wary from player to player.

On a different side on the same matter, by playing in the same group and with roughly the same people, you develop a relation to thoose players AND a reputation as well. For example, I will often prefer to work with someone I know to be reliable rather than one who is prone to beeing erratic/making nmr's and so forth. This provides a further challenge, due to the fact that reliable players are often that much better at the game itself - which can lead to some very interesting in-game discussions.