For reducing friction in the system, I don't know if it matters if a single pulley is used as the fixed or floating pulley in a 3:1 system; the fixed one is weighted much more than the floater, but more rope travels through the floater. It does make sense, especially if the lone pulley is a prusik-tender, to use that pulley as the fixed one to make the best use of the ratcheting prusik, since if the system is set up right that prusik would not have to be tended at all, even during re-sets.
I usually only carry one pulley (a Petzl Mini PMP) unless I'm on a two-person rope team, but do carry a DMM Revolver biner (the one with the small pulley wheel built into the biner frame) to use as an improvised pulley if I need one. So if I was setting up a 3:1 with just my gear, the lone pulley (with a very short ratcheting prusik that needs no tending)would be the fixed one at the anchor and the Revolver would be the floating "pulley."
If the $4 petzl is that little nylon wheel to clip into a biner, I've never used one, but have heard the same stories of them breaking.
Hope that helps.
OK. With the drawing, I understand your "drop loop" better: a 3:1 piggybacked onto a 2:1. in this setup I still say the best place for the pulley would be at the anchor, so #1.