Digital servos are supposed to be better for various reasons, holding power, centering etc.
The non corless will be fine for your edge, even a lot lesser servo will be ok.
I got the coreless for my Carden 30% extra just because I wanted the best I could afford.
You can never go wrong buying the very best servos, but you probably don't really need to spend the extra money unless you are into serious contest stuff.
The Hitec servos are programmable, using their servo programmer. From what I understand you can set and match centers, reverse etc., some people really like that function.

Don't forget , strength is the important thing if you are into 3D.