Chicago servers appease eastern, central and variably* (the five or six people in)mountain time zones including all of Canada.
Texas servers appease pacific, mountain and variably(based on location) central time zones - this doesn't benefit Canada.
I could go into depth on the actual network routing that NA deals with, however generally based on the network map of NA, Chicago remains the unofficial center of USA. If I had to pick the lesser evil I would stick with Chicago as it covers the majority of player population. If NA is lacking monetary support just post a request for donations and you'll get it.
note: Yes this is biased reply but not a biased message. I live in Michigan and of course would rather play on a 16 ping vs a 40 ish ping. However, many more will not be so lucky.
