It depends on your style. Were this my kitchen, I would look for something bright and light- probably modern, like those piston stools from DWR, in white or tan.

What other colors are using in the rooms around this kitchen? Is there a color or style that you like? I happen to love blues... They make me happy. Here are a few ideas.

Indoor/Outdoor 20.5"Lx40.5"H Rattan Bar Stool with Black Metal Frame · More Info

Worlds Away, Counter Height Stool With Velvet Cushion, Emmett, Brass Stool/Black · More Info

Avila Cheerful Blue and Multi Color Tufted Back Counter Stool · More Info

Counter Stool in Blue · More Info

Nikki Velvet Upholstered Stools, Set of 2, Pink · More Info

Flash Furniture Barstools Residential Barstools · More Info

GDF Studio Central Vintage Brown Faux Leather Bar Stool, Set of 2, Brown, Pu · More Info

Sopri Counter Chairs, Set of 2, Deep Blue · More Info

Anything with COLOR. And get some color on those walls too.

I prefer stools with a back and I too think that's the perfect place to bring in some color.

It looks like your space is neutral enough that you could go with any color. I could see yellow, green, red or teal working really well. I know a few people that have gotten their stools from Ballard Designs. They're definitely not the cheapest but they're good quality.