I like both, depending on their use. For sociability, the swivel are great. For writing or some other, more 'stationary' function, the stationary are it. The swivel is too much work to keep it stationary!

If you want the seats to swing out from the island be sure to check that the island is substantial enough to take the load, also that the island is well anchored to the floor. If you consider the arm is for example 2 feet long, then sitting on the extende seat will be the same as applying your full weight to a crowbar, two people sitting on one side would destroy a normally constructed island. Similarly, if fitted to a wall make sure that they are anchored well and that the wall structure is suitable. A nice idea to save space though

A Swedish company does this style which can be customised by colour, see below photo

Depending on what colour your kitchen hardware is, there a couple of options that would work well in a graphite kitchen. If you have white worktops and a grey kitchen, I would add another colour or texture to the stools to create another layer to the scheme. If you don't like using bold colours, you could use an interesting textured metal or wood for the stools. You could try using something similar to the silver wire stools below for a more industrial style Or wooden stools are always lovely for a more contemporary country look. I would use a lighter wood, to add contrast to the dark grey kitchen and white worktop All the best with your project