Sprint's WiFi calling isn't as robust as T-Mobile's. iOS has significant limitations for whatever reason on messaging. T-Mobile's international roaming is also better in terms of total countries covered, as well. Neither of the countries you listed have coverage listed by either carrier though. Their 50% off isn't as good as they make it out to be.

Do you have a phone that supports Band 12 LTE? T-Mobile has been doing a lot of "gap filling" with the low frequency holdings that they have.