I've used an Alpinlite and regular Helium.
The Helium is a top-notch bag, and possibly has the better hood. It lofts very well and has lived up to it's temp rating.
The Alpinlite (20deg) has been in very similar conditions and performed just as well. It may actually be slightly loftier than the Marmot, but it's a toss-up. It is roomier and lighter, although only by a small amount in each case (an inch or two and an ounce or two).
Why are you looking at the EQ version? I recently bought my first membrane-shell bag for winter use in a tarp, but in general I don't think they are a great idea. I haven't used that bag yet though, so I can't speak from experience yet.
Marmot's standard shell fabric is excellent unless you have special requirements from it. If you do, check out the WM Apache GWS – that's closer to the Helium EQ.
I have not noticed much performance difference between the two WM fabrics, having used their 0.9oz Extremelite and 1.15oz Microlite. I have not used their Windstopper fabric, but it seems very weatherproof and breathable, although heavy.