If you plan on breeding on a large scale you can't beat the mortar tubs. They are the least expensive way to get a lot of space in your rodent room.
If you are just doing things on a small scale I think that the cat litter pans are the way to go. They are more readily available and their consistency is better as far as the measurements and quality go.
The Jumbo Petmate litter pans are bigger than the CB30 duplicate boxes that Freedom Breeder and ARS use in their racks for breeding.
I really wish that I could find a place that would do a small run of custom tubs for me. That way I could really do what I want with my breeding and birthing racks, and especially my holding racks. There are just NO good tubs available for holding racks. Something 48" x 24" x 5" would be great. Any of the tubs that are large enough for a good amount of rats are always too tall for the little guys to get to the food and water.