Originally Posted by: CSchlegelIt depends upon the context of the situation.

Certain things are easier starting on downstrokes, and others on upstrokes. It totally depends upon the specifics of the notes and patterns you are playing.

Consider:

E |-8-7-5---------------|
B |--------8-7-5--------|
G |---------------------|
D |---------------------|
A |---------------------|
E |---------------------|

If you start this on an upstoke and continue alternate picking, then getting from the A to the G (changing strings moving down) you can use economy picking and play both of those notes with a downstroke. Makes it more efficient.

However:

E |-8-5-7-5-------------|
B |----------8-7-5------|
G |---------------------|
D |---------------------|
A |---------------------|
E |---------------------|

In this case starting with a downstroke makes getting from the A to the G easier with economy picking.

Also, certain situations might call for a heavier sound; use all downstrokes. Other situations might call for a lighter touch; use all upstrokes.

Make sense?

Everything depends upon context. :)