Asus is hit or miss, but they do have some good products. Lenovo when it was only thinkpad and owned by IBM had a sterling QA reputation then. Now, I don't know. My dad's company, bp, moved away from lenovo to dell for their computer business. I hear similar movements away from thinkpad as an industry standard in other fortune 500 companies. Take from that what you will. Lenovo always has the best prices for the features it seems. Some corners must be getting cut.
At any rate, I really despise the Yoga keyboard so as always try before you buy. I think the Asus ultrabooks are probably the best in class as long as you don't care about having a wacom digitizer.