Ive never pre-ordered. Is the app better than the web page to use? Also, if i am changing carriers is it better to use the carrier site (T Mobile) to order?
If you're changing carriers the process may be too complicated to complete during launch day.
In general, I'd use the app. Are you porting a number? Doing a family plan? Those may make things harder. If the past is a guide, you have around 30 minutes to get into the first batch of devices. It might be worth it to try and go through the process to see how much of a pain it is -before- launch day...but they usually do a credit check and you probably don't want that hit twice.