Optimal Video card settings?

Do I just leave the settings on my video cards at default or are there well known tweaks I should make?

I don't understand Aliasing and that other stuff.

One system has a Radeon HD 3870 X2 1GB

The other has a Radeon HD 4890 1GB

And the next one I'll use in my work area will have my older GeForce 8800 GTS 640MB

Not sure how much this helps, but just in case you don't know what anti-aliasing means...

http://en.wikipedia.org/wiki/Anti-aliasing

Now, what can your cards handle? I haven't a clue. lol