The app verification method is better - it helps protect against people being tricked into calling a fake number (through a deceptive text message, email or internet search).
If people can be convinced to use the app for verification, why can't they be convinced to use the app to find the correct number to call? I think the latter is much more natural for most.
I also like that I can skip a lot of the authentication steps by requesting a call from within the app - that way they already have a head start on identifying me when the call starts.
