Sno-Seal is what I've been using.

It's consistent, penetrates quickly and thoroughly, is readily available, inexpensive and (since made from bee's wax) allows the saddle to breathe somewhat.

Proofide is tallow, stabilized with citronella.

No matter what you use on a leather saddle, there will be some of the treatment that comes out as you ride. It's as certain as death/taxes. Not a big deal, unless you ride in expensive synthetic cycling clothing in a color other than black.