First off, there is a Tire & Wheel specific sub-forum, which is where this belongs. One of the mods there works for Tire Rack and he is very active in the forum.
It is a very bad idea to mix and match tire brands or models as the construction of the tires can vary significantly by tire model, even from the same manufacturer. This can lead to unsafe handling, especially in emergency situations.
For example, I had a 1990 300ZX I bought used, and it had one odd tire on the left rear. It was the same size as the others, but the shape of the tire was significantly different. I planned to replace them all but wasn't in a hurry to do so. That is, until one morning on my way to work I was taking this fairly sharp on-ramp at a good rate of speed and that left rear tire let go, at which point I spun 360 onto the highway. Fortunately there was no traffic passing by at that moment, or it would have been very bad. Needless to say, I got new tires for it within the week.
It's not that big of a deal to mix tires on that beater Civic with different colored doors you see on your way to work, but I would never do it on a car that I actually valued.