It depends on the size of the geckos. I have found that the large 6.75" deli cups are too large to ship a gecko in because it leaves too much room for them to slide around in during shipment. I use the 4.5" 8-oz cups for juvies, and 4.5" 12 oz. cups for sub-adults and adults. For shipping purposes, I use the cheapest, hole-punched cups from Superior Enterprise.
I use the 4.5 solo cups for shows, unless the gecko is large, then I use the 6.75 in 32 oz. Some breeders use all 6.75's and put smaller geckos in the 18oz size and stack them high.