Two great choices! But like said above, there are many points to consider...
The Front Engine Diesel (FRED) Cummins/Allison is a great choice - but that is the smaller Diesel engine similar to a full sized Dodge truck. GVWR should be 27,000lb.
The GM 8.1L/Allison is a monster (496cu.in.) V8 that is well suited to the task, with similar HP to the FRED, but lower Torque numbers. GVWR should be 24,000lb.
BTW: Both models had both of these chassis options when new.
The floor plans are very similar, but the 12' garage is obviously better. The extra 3 feet in the back is not a factor unless you frequent a campground with tight spots.
If it was me, I would give preference to the FRED. But in the used market, care and maint since new is most important.
When I was shopping to buy, I wanted a FRED-Bounty Hunter but could not find one with a reasonable price point.
So, I found a gently used Outlaw with the 8.1, and love it. The smooth angled roof easily cuts the rooftop airflow, and being a currently made brand is factory supported (Gulfstream has left the motorhome market).
There's info about these awesome RV's here:
Class "A" Toyhaulers