Leather New ... avoid it. I hate it. It's sticky, makes your tack sticky, dyes light tack, molds fast ... just don't use Leather New. It's horrible.
I really don't like any of the liquid type of conditioners. They just get a little messy. I like the more ... creams? I use Fieblings (sp?) Saddle Soap, in the little round tin. You can get em at TSC ;) Makes tack supple, soft, and doesn't mold ;)
When I worked in the restoration of library materials, (very old) many of the books had leather bindings. The only product we used on them was Lexol's Conditioner as it is neutral, being neither acidic nor alkaline.