Quote from abattia:
If you are a retail trader using a retail broker, you need to think about colocation proximity with respect to your broker's order servers (rather than proximity to an exchange).
If you are a retail trader using a retail broker and a retail data provider, then you need to figure out whether it's better to be near your broker's order servers or near your data provider's data servers ... or somewhere in between. Again, proximity to the exchange isn't relevant, I believe.
Now, another question to ask is how close to the exchange are your broker's order servers ... ?