Auto-negotiation is a lot more reliable than it used to be. So the folks who had to put up with its flakiness in the past say hard-code everything while the folks who have good experiences with it today say use auto. Generally, I think that auto on workstations and hard-coding on switch/router (up)links is the wise path. Servers sit somewhere in the middle. I usually leave those on auto, though some others like hard-coding them as well.
