I can tell you that I'm happy with my MSpeed exhaust.. cat back setup if you're wondering, that's how they come. If you're looking for a good tone, then this has it. I'm not sure about vibrant, but I've heard good things about them too. There are a few others; but I don't have any opinions of them. If you're after the warranty stuff, Mazda gives you a 12 month warranty on their CBE. Not sure about the other companies, although I'm sure it's the same...maybe?
It all comes down to your personal preference, and what you're after in the modding department. If you want to keep it "mazda" for the most part, go with the speed brand. If that doesn't matter, go with either one. They'll both offer the similar performance and different tone over stock. But its until you delete a cat or go with a hi-flow cat is where you should notice any bigger gains. Hope this kinda helps. Anyone else want to chime in?
-J