No preference. Aesthetically I prefer snakes, but when I'm fishing I could care less.
I rebuilt two rods this winter and used the guides from the original rods for each. One has snakes, the other single foot. Both keep the line where it should be on the rod, and I've never had issues with line wrapping, guide bending, etc. To assess whether snakes have a noticeable impact on a rod's action you'd have to cast identical rods with identical setups except for the guides. Has anyone done that? (that's a question, not a challenge) Depending on the blank and desired action, you might find that the "theoretical" stiffening you get from the double mounting points of the snakes results in a desired action. Again, only side-by-side casting would tell.
Building-wise, the snakes took slightly longer for obvious reasons, but I found it easier to get the snakes exactly where I wanted on the rod. I was able to use a decent-sized piece of masking tape to hold one side of the snake in place, so the guide didn't move or twist when wrapping up onto the guide from the blank. With the single foots I could only use a thin strip of masking tape, also for obvious reasons.
EG