Rear hex drive nipples were designed to handle increased torque but they also prevent builder’s marks on external nipple wrench flats. Some people like rear drive because the turning direction is intuitive — clockwise is tighter. Since the external interface exists just the same, you can forget the rear hex drive if you prefer (or treat it as a backup to save the day if a nipple cracks or rounds off).
What many hex nipples lack is a screwdriver slot. This is important for compatibility with depth-setting nipple drivers, the fastest way to preload nipples to the same depth of thread. That’s why SpokeService specially imported a Sapim hex nipple with this feature. The first photo below shows a collection of adjustable depth-setting drivers that interface with the slot. The black Problem Solvers tool with a 6000 bearing pressed on the end is my daily driver. (If your nipples don’t have a slot, you can start your nipples visually or build a universal tool — both inferior solutions.)
The Sapim hex drive is 5.5mm. It’s a balance between making the interface as large as possible while leaving room for tool clearance at the rim holes. Even so a thinwall tool is often necessary. I have three in my toolbox. My main tool is the Park SW-15, a 3-way that fits nicely in the hand and provides good leverage. Blue tape marks the 5.5mm end. The Park Tool SW-18 is a screwdriver design, which reaches into deeper rims and may fit better in race toolboxes. The Sapim factory tool is excellent quality and handles even deeper rims but may be too deep for everyday use.