That tends to depend on the setup you've got, and what level you're focusing at.
Either way, within the rack, is East/West, but if you're looking at things on the rack level between racks may not necessarily be so:
- If you've got a cross-connect between racks, then that would be East/West.
- If your traffic has to transit your rack's main uplink (i.e. contends with "true" North/South) then that would be North/South.
Having a cross connect is wise, but by no means a given.
On the other hand, you're the D/C operator, then you're going to view it all East/West because it's not leaving your DC.