Horizontal stacking – “most obvious / common”
Vertical stacking – has benefits for > 1U sizes (e.g. long PCBs in a 2U)
Perimeter arrangement – lots of room centrally, more difficult to rigidize PCBs (they flex relative to one another), no ability to stack connectors
Connectors vs. Wires
Wires are more likely to fail simply because they are more complex – endpoints, crimps, chafing, etc.
May be best solution for certain applications (e.g. high-current runs, solar panel connections)
Point-to-point wiring is theoretically optimal in terms of minimizing mass, but practically speaking it’s a big problem, esp. in assembly / disassembly