Some not-very-well-organized thoughts, from my brain to yours...

NHP makes their "Sport II" Concept blades in 3D and normal flavors. They have the same airfoil, the only difference is the weight - standard blades are around 95 grams (105 with covering), 3D blades are 75 grams. Autos are more of a challenge with the 3D blades, but it rolls a bit faster and the hover is a bit more twitchy. Personally I think my Concept rolls plenty fast enough with KSJ paddles and the upgrade seesaw, so I went back to standard blades after just one set of 3D blades.

Modelsport's 30-size blades used to be available in 3D and normal versions, I don't know if they still are. The normal version had a simple airfoil much like NHPs (but not the same), while the 3D versions had a reflex airfoil. If memory serves, the weight was the same. I didn't care for the 3D versions at all. Collective was very twitchy in a hover. They autoed a little bit better and I think the top speed was higher, but the twitchy response just annoyed me.

Some FAI/F3C blades are asymmetrical, which makes sense because the heli is upright for 90% of the F3C schedule. To the best of my knowledge, all 3D blades are fully symmetrical.

Personally I think it's a mistake to label "twitchy" blades as "3D blades." I'd much rather have smooth predictable blades for 3D flying. For a while I was very keen on faster roll rates, and I think that's a phase that most everybody goes through (it does wonders for your confidence if you know you can get out of trouble in a hurry), but IMO "good" 3D is about precision, not twitchyness.

Many folks opine that 3D means low-to-the-ground inverted stuff, so again twitchy blades are not necessarily the best choice. The closer you are to the ground (not to mention your body), the less room there is for error - precision is crucial.

I spent 90% of last summer flying 3D with TG 690mm tapered blades (MA sells some identical tapered 690s with their "Rotorsport" sticker), and that's something most people would call an FAI/F3C blade. It's symmetrical, but you have to spin them fast to get much response out of them. I like them just fine.

I wonder if you asked the big-name 3D pilots what sort of blades they prefer, how many would ask for reflexed airfoils and low-mass or inboard-cg blades?

My guess is not many.