If your concerned about passing smog, stick with just a cat back. Once you start swaping parts before or the cat its self, your rolling the dice. I can't say which exhaust will get you the most performance gains, but look for the ones with the following characterstics and there won't be huge differences between them;
1. three inch piping
2. minimal bends
3. muffler (and resonator if included) with a perferated core and "full" three inch internal diameter. Some systems out there step down to a smaller diameter and have louvered cores that reduce flow, especially in the resonator. Ask before you buy. If they can't answer or don't know, don't buy it.
Looks, material and weight are up to you and your wallet.