A Legal Warning:
The following is just MHOs and may or not be true.
I find that a scalloped top, Acoustic Guitar, has a more open or vibrant tone when new and right out of the box.
After years of play a non-scalloped Guitar may achieve a comparable level of open tone.
But I cannot say one brace design is better than the other.
Because it has a lot to do with musical and playing styles. So, I have multiples of both designs.
When I am finger picking,(without picks), I prefer a scalloped top guitar, it delivers more of everything. Also good for light gauge strings. Exp: couch or coffey-house playing on a LG-2, D55, HD-28V, ect.
But when I am cranking down with a heavy flat pick, on medium gauge strings I really prefer a non-scalloped top guitar. I get the volume and tone from my hand action. EXP: Jam,Bluegrass,ect.on a D25,D-18 or D28.
Although anything can be played on any type of guitar,( note Willies Trigger), different Guitars and design features, for different types of music and play styles are great, its just that each of us must arrive at what we like.
Try them all...find your sound.
Dale.