As a baroque violinist, I encounter double, triple and quadruple stops, like in Bach, Telemann, and Biber, and I want to articulate them correctly. I am looking for advice on how to break them, and how to decide which notes to emphasize.
I'm only an amateur on the violin, but for simple chords, you break the notes up into two groups, with each group sounding two strings. For example, a quadruple stop would first be played on the G and D strings, then the A and E. A triple stop on the bottom three strings would be G and D, then D and A.
For music where some notes in the chord change and some are sustained, it's largely a question of what's physically playable, and where the melody notes are, though it's more difficult to figure out in more complex works. Bach's unaccompanied violin pieces in particular are interpreted differently by every performer, and there's a lot of nuance that goes into figuring out which notes to emphasize.
You should decide which notes to emphasize by understanding which notes should be emphasized if there were no double or quadruple stops.
For example, if the lowest note is participating in a melodic figure that should be prominent, then it should be prominent in the chord. If the highest note is participating in a figure that is the main part, then it should be prominent (and likewise intelligibly connected to its sister notes in that main part).
If you are not sure what to do, then you ought to study the score more until you are. Or you can try different ideas and see if they make sense.
One approach I would decidedly avoid is to box yourself in with an arbitrary rule, like "in Baroque practice, the bass note should be emphasized." Even if such a statement were penned by a contemporaneous performer, we should step back and realize that A) it's possible people from the time were wrong, or bone-headed, and B) making yourself subservient to a rule that is divorced from the musical outcome or result that you are trying to achieve as a performer transforms you from a creative artist into a boring robot!
So, understand the musical function or role of all the notes in the chords (are they melodic, accompaniment, participating in various step-wise motions in subsequent events?), and then structure the loudness of your playing so that it is aligned with these roles.
In fact, this approach will work very well for all the notes in the piece, not just the double-stops. It bears emphasizing:
Align the loudness of all the notes to fit their role in the musical motion indicated by the melody, harmony, rhythm and texture fixed in the score.
Do this in such a way that the sounds unfold intelligibly, with a musical energy whose increases and decreases are balanced, and a great musical experience might just emerge! Good luck!