Ok lets clear one thing up. Overdrive causes distortion to a degree so overdrive will come first.

Try this if you don't beleive me. Put your stereo on pick a fave track and play at your normal volume, then whack the volume up full and listen and you'll hear the sound is distorted. What a distortion pedal does is distort the natural harmonics in a note so they are pushed through they are based on the orriginal fuzz face pedal for the most part. Overdrives increase the output of the guitar signal so if you increase the amp gain you'll get natural distortion with the overdrive. As for tone. Go overdrive all the way and forget the distortion pedal all together unless you are in to grunge or really dark metal. Distortion does have it's place but i would allways go overdrive first for that slightly distorted sound and to increase sustain.