I am aware that wikipedia has a nice list of olive varieties including tastes (sometimes). However, I'd prefer a considered answer, so this is the place.
I'm looking to substitute based on taste, not looks, as my local supermarket has messed with its Kalamatas and I don't find them nice anymore.
Googling indicates Gaeta, Amphissa, Nicoise, but it's an ambiguous mess.
I use a vinegar + brine-cured variant. What is the closest taste approximation?