I like the Schroth belts personally. Sparco/Sabelt are nice as well. It's a tough one because all of the belts work well. It's just a matter of what features you like better.
What I liked about the Schroth is that they were FIA approved (European Standards). The FIA is stricter with their guidlines for safety IMO. They do more crash tests to test belts than the SFI (US Standards). The SFI is more concerned with design requirements (belt thickness, etc...) Plus, Carl Schroth being a German, you know that he is going to be anal about things.

Those German engineers... Heh.
The other thing that I liked about Schroth was their cam lock system. I thought that it was superior to anything on the market. Schroth also has a ASM system (anti submarine system). What it does is add extra material on the inboard shoulder belt that is designed to let go before the outboard side and put your body into proper roll position in a crash. I don't always wear the 6 point (anti sub belts) and it's nice that this system is designed for use without a anti sub belt. I'm not saying that the 4 point ASM is superior. I'm saying that it's better to use the 4 point ASM than to use a non ASM belt system as a 4 point or to incorrectly use a 5 or 6 point system.
One thing that I wish that the Schroth belts had was a sternum strap. I know that they probably don't believe in using their belts with a sternum strap. I asked the question about the stock Z06 seats without the pass throughs on the seat backs and they just told me to get a seat that has pass throughs. Same with their anti sub belt system. They'd rather have me not use one than use one incorrectly, i.e., put a single anti sub strap over the front of the seat cushion. Carl Schroth is not only concerned with design and testing, but he is also very concerned that his belts are installed and used properly.
I want to mention one of the problems that I have with the SFI. Schroth makes a belt system with a 2" lap belt that is FIA approved. Schroth found in testing that the belt actually fits the human anatomy better and when there is a crash, there is less damage or injury in the pelvis region. The SFI doesn't seem to care about these findings, so a 3" lap belt is the standard with SFI even though the 2" has been found to be superior. I went with the 2" lap belt system. I'm fine for DE's and some club racing, but some racing governing bodies also require SFI certification. This belt would not be legal.
Anyway.. Sparco makes a nice belt system as well. It's also FIA approved. I don't think that the cam lock is as nice, but it's still a quality belt system. Their belts are also available with a sternum strap if you need it.
The biggest problem with the Z06 seat is that it doesn't have pass throughs on the seat back and seat cushion. The best thing would be to use a race seat. If you aren't going to use a race seat, you have to make some comprimises, even though they aren't the safest options. For example, probably the best way to use an anti sub belt on a stock Z06 seat is to use a 6 point (dual anti sub strap) system. What you do is clip them in or bolt them in, sit on the straps and clip it between you legs. It's certainly not the best solution, but it's much safer than running a single anti sub strap up in front of the seat cushion and then clipping it into the harness.
I don't know where I'm going with this post.

It's already getting much longer than what I wanted to write. I guess any belt systems going to be relatively safe. Just make sure that you use it as properly as you can.
Other manufacturer's to consider.. Crow, Willans, Deist, Simpson, Ge Force.. Read up on them. Find out about their features. Decide what you like. Any of them will probably work just fine.
Just remember, that you'll probably want a 6 point system if you're using stock seats. Clip in style belts are nice because you can take everything out when you're not using them. If you're going to race, make sure that your belts are SFI approved if you're here in the US. It might be a good idea to look for a belt with a sternum strap if your seat back doesn't have pass throughs. Though.. I don't use a sternum strap. It's debateable if that's safe or not.
Have fun, be safe.
X