Engadget’s review of some roaming data SIMs shows that SmarTone’s Roaming Data Pack service (at around $22 for 50Mb) is pretty poor value.
That said, I’ve never been asked to top-up while abroad, but that may be because I signed up for the package when it was still “unlimited”.
But SmarTone will most likely win out, because it is so easy: no SIM swapping, your mobile number still works (although I guess you could divert calls to the new SIM), etc
.