K&M 14076

I've bought this keyboard bench in december 2012, when I started playing keyboards. With my Nord Electro 3 61 and a K&M 18810 stand, I had a nice, high quality setup. "Assembling" it took only one or two minutes, since all you had to do was finding a height that is comfortable for you and use a screw to fix the bench in place. However, you should be careful with that since the screw tends to get stuck a little, making it hard to adjust it afterwards.
Like all K&M products, it is pretty sturdy and will probably last a few decades, a rare feature nowadays.
The cushion is comfortable enough to let you play your keys as long as you want.

There are cheaper alternatives on the market, but I would definitely buy it again if I ever had to.