Moved your post to Dyes, Antiques, Stains, Glues, Waxes, Finishes and Conditioners. It really has no connection to Hardware!
You need to provide more information. It's sort of like asking "What colour should I paint my car?"
You need to tell us what you want the conditioner for and what you expect it to do for you. What kind of leather, what is the item used for, what weather or work conditions is the item subject to? None of us here have a crystal ball to see what you actually want.
Once you give us some details, someone will be able to help you.