All varieties of cucumbers can be used but some are specially bred and give a crisper result. These usually have pickling on their label or advise they are good for pickling but varieties will vary depending on where you are,
In the UK varieties include Venlo and Parisian Pickling. I am also aware of varieties such as Pioneer, National Pickling, Saladin, Bush Pickling, Ballerina and Boston Pickling,
Pickling cucumbers usually have thinner skins than the salad type, which allows the pickling solution to better penetrate the skin and flavor the flesh They are short and relatively wide and tend to be bumpy rather than smooth. Remember to pick cucumbers relatively young. A good pickling cucumber will have fewer seeds at this stage but this will change if they are allowed to mature and ripen.