I've also found myself frustrated and confused over the debate on whether 2-ply reso heads will muffle the sustain or enhance it! Anyways...
Ambassadors (usually clear) seem to be the standard when it comes to reso heads for toms. I'm in the process or replacing the reso heads on both of my kits (10 toms in total) and I'm using clear Ambs on all of them. They're just 'The Standard' and I believe they're that for a reason. Keep in mind that you're using Pinstripes as a batter head which will also 'deaden' the sustain of the drum a bit.
I have an idea though that may work for you... since you mentioned you wanted a shorter sustain for your drums, why not try using a Powerstroke 3 head for the reso! It's just an Amb with a built in dampening ring and you can get them in clear or coated. That way you don't have to fret over the 1-ply or 2-ply debate for minimizing the sustain. I've used them before as batter heads and they were quite good, so worst case scenario, if you don't like it as a reso you can keep it as a back-up batter head if you break one, or if you want to try them as batters for the whole kit at some point down the road, then you've already got one of them.
Of course, there's aso the Powerstroke 4 which is a 2-ply version of the Powerstroke 3 (basically an Emperor head with a built-in dampening ring), and the Pinstripe which is also 2-ply, but not free-floating 2-ply like the Emp. or P4 and the Pinstripe also has built in muffling but not in the form of a dampening ring (I believe it's a ring-reducing agent of some kind instead, maybe an oil?).
I guess you still can't get away from the 1-ply VS 2-ply thing entirely, but I'd say try the Powerstroke 3 cuz it will definitely shorten the sustain and you can avoid the debate for the most part. Depending on where you buy, you might be able to return it if you don't like it since you won't be putting any marks on it due to it being a reso head.
My $0.02 - All the best,
Mike