Any of those would work, but the Alps & Marmot are getting heavy. BTW, the EMS you linked to is the long version.

What area and conditions will he be using this? In other words do you really need 20 degree?

Also keep in mind that synthetic insulation will lose about 30% of it's loft fairly quick so what started as a 20 degree bag (if it was accurately rated to begin with) will be closer to 30-35 after a year's worth of monthly outings.

Seems Kelty no longer makes the Light Year series. I'd probably go for an REI Lumen or North Face Cat's Meow (both should be 30% off during their anniversary sale in another week or so).

I think you'll get some benefit from the paper I wrote geared to new Scouts. Should help you from blowing money on gear you don't really need.