I am sure foil helps more with the stall, because it doesn't breathe and thus creates much more of an oven effect than the paper ever could.
I have not SxS tested with and without paper, but it seems like the paper method gives me the best of both worlds. I don't end up with a mushy bark at the end, it "seems" like it still pushes through the stall faster than nothing, and I get a juicy hunk of meat. I don't know if this makes any difference, but my paper is pretty thick and by the time I wrap in paper it ends up double-wrapped...one piece the long way underneath the meat, and another one the short way across the top of the meat. I try to do one, but I'm never happy with how it "seals" with just one big piece -- and I just use probes to hold it all together, or the top piece ends up with ends trapped underneath the roast.
I am sure there's a video of someone testing these theories out there -- I vaguely think watching one sold me on buying some paper and trying it out. As with anything, YMMV.