UT and RT effectiveness is similar, but each have their pros and cons.
Whether or not you can present an approvable case for revision to the customer depends on the type/orientation of defects you're specifically looking for.
For example:
If porosity is a concern, RT is better.
If hairline cracks are are concern, UT is better, with limitations on crack orientation.
Some highly critical inspections require 2 or 3 differing NDT methods for ultimate assurance.
There is a boat load of info about this and more in the archives of this forum. I recommend a search.
Here's a good place to start:
https://app.aws.org/forum/topic_show.pl?tid=18583