If you've had the same problem with 2 different brands of tires, then the problem is not the tires and changing tires is not likely to fix the problem.
First, start by getting an alignment. Find an alignment tech who agrees with this statement: The factory alignment tolerances are too wide by half.
Once you have found him, follow his advice.
Next, try to avoid high speeds and over loadind. Also try to use more inflation pressure. On every vehicle sold in the US, there is a sticker commonly - called the vehicle placard - that lists the original tire size and the proper pressure for that size. The placard is usually located on a doorpost or in the glove box ? but sometimes it is located in the trunk or on the fuel filler door.
Use 3 to 5 psi above the placard pressure - assuming you are using the placard tire size. If you aren't using the placard tire size, then post back. That might be your problem!