Ideally, if Thomas's surgery technique had more consistent healing results, it would be the golden standard since it alters both pitch and resonance, but clearly that does NOT happen. Lots of the "after" samples from that surgery end up sounding extremely raspy, or like there's constantly phlegm in their throats. And that happens with a lot of the more invasive surgery techniques.
So yeah, I agree with Jenny, right now Yeson is probably the best option. I haven't heard a single bad "after" sample from them, just maybe some that it didn't change enough.