Depends on the flash we’re talking about. The Asymmetrical belt is better for Barry and the symmetrical belt is better for Wally.

The split belt is a bit overused, everyone uses it nowadays. but it's probably more comfortable.

Symmetrical belt

If it is more like a physical belt or removable then definitely the symmetrical, but since the flash mostly has the belt simply as part of design and its just recolored from the red, I have to go with the split belt