I'm working on an open sight/scope setup that will utilize quick detachable rings w/scope and a peep sight (Skinner Lo-Pro sight) on my Marlin 1894 .44 mag. My question is "What QD rings work well to return to zero?" Also, do they require a steel Weaver rail as opposed to the aluminum rail?

I have Leupold rings on my .35 Rem. If you can live with plain ol' thumbscrews instead of fancy levers, then the usual Weaver rings will serve the same purpose. Guess it just depends on how fast you plan on needing to be able to change them out!

And I've always used the Weaver 63B (aluminum) bases.

I've been using Warne Maxima QD rings for over 20 years. Now, most good QD rings will return close enough to zero at 100 yards, but try them at 500 yards and that is where the real test is. I have removed the scope from my LR match rifle several times and then returned it to the rifle and it has always held absolute zero at 500 yards. You cannot beat that with a stick and for the price it is a can't lose choice.
You should use a steel rail if you want the best case situation.
My son's 1895SS is set up with the Brockman (http://www.brockmansrifles.com/sight_options.asp) Gen III front (cut with old .750 hole spacing) and rear peep sight with a Leupold Scout scope held in Warne Maxima rings on an XS scout rail (http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=515753&t=11082005). It never loses zero even though it is an aluminum base.

I don't trust 'em. I do one or the other and put 'em on with blue loctite.

.............Warne Maxima QD's on an XS rail, here. They do return to zero! Follow the mounting instructions and you will have no problems.

.............Warne Maxima QD's on an XS rail, here. They do return to zero! Follow the mounting instructions and you will have no problems.

Yeah, Flat Top, just like that. What scope is that, and are those low, med, or high rings?