Definitely walk. I'm not entirely opposed to the TrAAin if it's the end of a long day and you don't want to walk.

However, I agree with everybody else that it is a VERY BAD IDEA to get on the TrAAin if you have a quick connect time. In the past year it has "broken down" twice with me aboard. In one of the cases I was trying to get to my flight to MEX in Term A with 30 mins to spare. Boy, did I learn my lesson! I actually made it to the flight but I was dripping with sweat and my heart was pounding.

Since then I have never used it.