I have always liked Yamaha. I rode a Kawasaki KLR 650 for a long time, and in fact still have it.
But if I have the choice, I will always go with Yamaha.
Simple, they are designed well, in my opinion the quality of the machines is 2nd to Honda.
Also, they are SO much easier to work on then many of the other manufactures. Typically, to work on a Yamaha, all you need is a metric wrech set and metric socket set. Yet on Honda's, you need all sorts of special tools to dis-assemble the engine. Some of the special tools are only availible from Honda.
Also, when comparing my wife's Yamaha TW 200 to my Kawasaki KLR 650, the Yamaha is so much better engineered in my opinon. The parts that need serivced regulary are easily accessable.
Kawasaki makes a fair product in my opinion. When considering the bang for your buck, Kawi's are pretty competitive. Though they use a chain driven engine balancer that needs regular maintnance instead of gear driven. I have ran some really old Kawasaki 2 strokes, and am happy to report they all ran extremely well.
Suzuki makes pretty good engines in my opinion, but I have never been impressed with the transmissions. I ran some old Suzuki 2 strokes and had alot of serious problems with them.
KTM is simply, too expensive for my blood. They make some really great bikes with lots of horse power. But they are too expensive and the operating cost of these bikes is pretty high. Synthentic oil only and changing the oil every couple hundred miles, no thank you!
BMW - No thank you, I believe only royalty drives BMW. I am not royalty and don't have enough money to buy one, I will pass
Harley Davidson - They are pretty, and sound cool. But they are very expensive and I will NOT become a chromer (Ride a couple miles, sit around talking about the latest chrome parts we purchased, showing them off) I want to ride, not sit and chat about who spent the most on chrome.