Finally figured it out. While I like the finished portions of both pairs of socks, the ironwork design on the black/grey/white pair is fiddly so I don't want to touch those unless my brain is 100% there. The other pair is plain knitting so a no-brainer and I quite like how the colours look in the fabric but they are boring TO knit. Perfectly predictable which is going to come next and how many stitches it'll be before it changes again. Right now what I really need is something that has me wanting to knit more rows just to see what happens next.
So the predictable multi-colour pair have gone onto "storage" needles and I dug out a couple of Crazy Zauberballs and cast these on last night. Sock enthusiasm returned so fast I'm amazed it didn't give me whiplash. Those two balls of yarn really are exactly the same colourway, but the joy of Crazy Zauberballs is the pure randomness of the order, length, and combination of those colours. The fiddly shaping of the toes is finished and I'm now a few rows into the round and round of the foot portions of the socks, including narrow clocks up each side in an Austrian twisted stitch pattern called "Wheat Grain" (currently hidden under the curl of the top rows of stitches but it'll be visible later)
This is my second pair of socks from these particular balls of yarn; the previous pair were knitted in the opposite direction so the toes of these begin at the colour where the toes of those left off. It's entirely possible that I may get a third pair out of this yarn and I'm loving that fact that no two of those socks will look exactly the same. :-)