If you are moving bits from $External_DC to AWS, your best bet is to colo inside Equinix (or equivalent) and use their cross-connect to AWS service. If you have 100 fiber interconnects between you and AWS, you can move a lot of data (it becomes an interesting programming problem to figure out how to saturate that much fiber consistently).

In terms of your customers getting data to you, again, fiber interconnects inside the DC are your best bet. Colo'ing is the fastest way to move bits because it relies on arteries, not capillaries, for moving bits from place to place (no last mile problem).