I feel i've written on this topic so many times that even i dont understand it anymore. There are quite a few threads around... Basically you only ever want hard edges where your uv islands are, anything else is going to cause artifacts. So if you plan on using a lot of hard edges, you need to plan on spiting up your uvs…
U've got a lot of problems with your normal map...and that because u didn't used smoothing groups(hard edges in maya....really dunno what software u use). Here is an example how the normals should look like.
Listen to EQ he is SOOOOO RIGHT, this piece of advice let me COMPLETELY fix all errors on my glock18 and he has caused me to get into subd modeling in maya which is great fun and it feels very cool to be able to accomplish, in practice though what i've found easiest (for me) is to unwrap like usual and then once finishing…
In terms of the smoothness of the low poly's - I think it's coming back on the normal map, it actually quite obvious that smooth parts are looking kind of choppy. The main bath tub body looks a little noisy and looks like it has some hard edges. The cylinder, where it bevels to the thinner part there is some noise in that…