My hunch.....a 3 blade will fly "faster" compared to a comparable 2 blade.
On my 40%, I'm using the Mejzlik 32x10L.......that was the prop of choice back when the DA150 was the only engine to have.
Now, a lot of guys are using 30x12 instead.....I haven't tried it, so I don't have first hand experience to report.
On noise sensitive fields, the larger 32 can rip (tips further out) and make more prop noise.
A 3 blade would further reduce this.
But, a smaller thrust disk, might take slightly longer to punch out, and downline braking would be faster.
Either the 28x12 or 29x10 would probably be fine......
I have a DA100 (original from 10 years ago.....when they were "new") and normally ran a 27X10
I bought a 28x10....but never used it, and recently sold it to my friend.
I switched to a Zoar 26x12 (being rusty on my flying, I tapped the tip of my 10 year old Mej) and wanted that extra 1/2" ground clearance.
I can't compare the two, because one is wood and different brand, but, they both work fine.
I'd have to suggest, call DA, and get some of their feedback, and ask more guys that are running the DA120 what prop they are using for 3D and Sport flying......even more helpful, if they are using the same airframe too.