To me personally, Amego is better.
Slightly larger brakes, more power, faster, more torque for climbing, little bit cheaper, etc.
The only good thing about the Surface 604 is torque sensor (although I prefer cadence sensor because I like zippy bike than "natural feel" bike, when I ride ebikes with torque sensor, I really can't tell whether or not motor is actually doing anything) and better front suspension. But Amego has suspension seat post.
That said, I think they're both great.
Watch this video @3:00, when he talks about how little effort it takes to activate hydraulic brakes, he's not lying.
My mechanical brakes required so much effort, it sucked so bad. I know I keep saying this but hydraulic brakes are MUST HAVE.