The Connelly Hides are dyed in a vat. They are porous, and will drink in the treatment. These are in high end cars. Connelly Hide Food is recommended.
Finished leather is in the bulk of cars. This is leather that has in essence been spray painted on. They require less treatment, but are less durable, and less able to drink in the treatment. Finding a treatment that will be absorbed is difficult. I have used leatherique once, and it is due for another treatment soon. I will not say this is the best, as others have used other products with great success.
There is on thread in which someone filled in cracks and dyed the seats. It is quite an interesting read.