The thing about most of these memory cards is, they either fail immediately or they live forever (almost). So if you are buying from a good retailer, you can try it out extensively for a week or two and see if it is OK. If it fails, you can send it back immediately. This doesn't mean they just dont fail after a month, but if it doesn't in the first month of good use chances are much less. I wouldn't worry about buying a Kingston from a good retailer. In fact, I have had one (4GB version) for a while now.
Buy what is on sale. 133x is plenty if you don't shoot bursts of 15+ shots or are using it for video.