Caran d'Ache pastels are probably the hardest of all the pastel pencils. They are also larger in diameter than the others, so you'll need a wider sharpener.
I love these soft pastels. They are smooth, vibrant, and seem to have less dust than other brands. They are also MUCH less expensive than other brands.
To protect soft pastel drawings and seal them to the support, use this resin-based and alcohol-based solution, specially formulated by Sennelier for use with soft pastels. Sennelier Latour Spray Fixative for Pastels leaves the subtle hues of pastel colors unaltered.