Which is better, AT&T or T-mobile while I'm in Mexico?

[soccermaniac]

I will be traveling to Mexico this summer and right now I'm on AT&T but I will be switching to t-mobile later. Should I switch before or after I go?
Which one has better coverage?
Which one has better pricing for international usage?

Thanks

[Papi]

not sure about the cost because all will depend of your actual plan, however both companies will be connected to TELCEL, I would like to suggest you better to buy a cheapest one at the moment you arrive to México and will be very cheap for you, specially if you buy some MOVISTAR is the cheapest one and good coverage!

[Unregistered]

For choosing your sim card,Go to a phone shop in town, tell them what you want, they can advise.Before getting your cell phone service provider,Make sure your phone is unlocked and accept that carrier,If it's restricted by other network carrier means,You will need to unlock your phone.For unlocking you can approach your current network provider or else try to buy an unlocking service from any one of the online unlocking service provider like Unlock-Zone.com and you can get free unlock instructions from MobileUnlockGuide.com I hope it will be very useful to you.