The general opinion is that bar stools with backs are more comfortable than the backless ones. It’s quite logical actually. Having something to rest against is definitely comfortable and even ergonomic, especially if you’re sitting on the stool for long periods of time. Backless stools can be comfortable too, usually if they’re only used periodically or for short periods of time.
Another good example of simple design that fit in a variety of interior designs is that featured by Stool_One by Magis. Here you can see it displayed in a contemporary setting where it complements a large kitchen island.
Wood, plastic, fiberglass. What your bar stool seat is made of can be anything, really. Not that this fact makes your decision any easier. But if you’re stuck, think about practicality if you want to be able to wipe it clean, something non-upholstered might be the way to go.
Once you got all measurements right, you need to decide how many stools you need. Figuring out the number is easy. You need to provide adequate spacing for people to eat, drink or socialize. A distance of around 26”-30” between the centers of the bar stools should be ideal.