'Zuki makes a comfortable ride, for sure, and a decent machine generally. (Soaking the 400 Eiger which was only a month old upside down in the Bering Sea didn't improve the performance, but, other than various electronic components, it didn't kill it either.) Mine has more than 25,000 miles on it and it still runs - at least during the warmer months when I drive it.
For very solid engineering however, the Grizzlys seem tough to top. I was a devout Honda user for years, and I still work on them, but it seems that is what Honda has become. Yamaha has many features from a design standpoint which are better than most. We've only run our 450 for six months; not a lot of miles in the cold, but it still starts at -15-20� F. Presently it has only 3000 miles but it looks like it'll be around for a long time. I liked the idea of the sealed-in-oil rear brake system since both Honda and Suzuki rears are very reliable in giving up when they've been around the block a few times in our conditions. Additionally, the belt drive system is rock solid in so many ways which most engineers overlook. The ride feels different than others I've ridden (I prefer solid rear axle on roads/hard trails) but I'd buy a 450 or 550 again in a heartbeat, assuming that heart beat included $8K.