For this attempted fair comparison, I attempted to get the smallest file without sacrificing image quality. For most of the images, I viewed the original and preview at 2x magnification to get a better idea of what was changing.

I found that I had to stay much higher on the Fireworks scale, as we saw in the second test. I also found that in Fireworks, anything below 80 quickly introduced artifacts and "blocking" where parts of the images would start to look like squares.

We see here that it's a dead heat. Half of the Fireworks images are smaller, and half of the Photoshop images are smaller.

Photoshop: 23619 bytes
Fireworks: 53399 bytes
Photoshop: 42517 bytes
Fireworks: 102512 bytes
Photoshop: 33773 bytes
Fireworks: 51838 bytes
Photoshop: 61055 bytes
Fireworks: 59792 bytes
Photoshop: 119762 bytes
Fireworks: 88144 bytes
Photoshop: 47942 bytes
Fireworks: 28977 bytes
Photoshop: 61632 bytes
Fireworks: 36535 bytes
Photoshop: 18432 bytes
Fireworks: 36087 bytes
Photoshop: 16829 bytes
Fireworks: 26834 bytes
Photoshop: 42723 bytes
Fireworks: 26566 bytes

Photoshop total: 468284 bytes
Fireworks total: 510684 bytes