Everybody has their own sense of aesthetics, so ymmv.
But I wouldn't say that the Aeronaut has a "duffel style" shape. Quite the contrary, when in use it looks like a soft-sided suitcase (which it is). Think Tumi, but designed by someone who understands how bags work.
And I'll second Lotuseater, it holds its shape remarkably well when under or over-packed. I, too, started out with a ca. 2003 MLC. It was easy to pack, but couldn't hold its shape and everything wrinkled. Packing the Aeronaut took some getting used to, but the physics of how the bag carries and holds its shape have won me over.
And I love the split handles for carrying a sweater or jacket--I would never buy another bag without this feature. (So hearing above that the Tristar handles don't work this way will probably keep me away...drat!)
Oh, and the end pockets are great for stuffing (and forgetting) dirty laundry.....
But as I have said elsewhere on the forum, if you travel with a laptop, it will fit in the Aeronaut, but is just a bit difficult to get in and out. The Tristar trumps it here.